* [PATCH 1/4] doc: Rename LOCK/UNLOCK to ACQUIRE/RELEASE
2013-12-18 19:08 [PATCH 0/4] arch: Introduce smp_load_acquire() and smp_store_release() Peter Zijlstra
@ 2013-12-18 19:08 ` Peter Zijlstra
2013-12-18 19:08 ` [PATCH 2/4] arch: Move smp_mb__{before,after}_atomic_{inc,dec}.h into asm/atomic.h Peter Zijlstra
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: Peter Zijlstra @ 2013-12-18 19:08 UTC (permalink / raw)
To: linux-arch, linux-kernel
Cc: geert, paulmck, torvalds, VICTORK, oleg, anton, benh, fweisbec,
mathieu.desnoyers, michael, mikey, linux, schwidefsky,
heiko.carstens, tony.luck, Peter Zijlstra
[-- Attachment #1: peterz-arch-Document-v2.patch --]
[-- Type: text/plain, Size: 18241 bytes --]
The LOCK and UNLOCK barriers as described in our barrier document are
generally known as ACQUIRE and RELEASE barriers in other literature.
Since we plan to introduce the acquire and release nomenclature in
generic kernel primitives we should amend the document to avoid
confusion as to what an acquire/release means.
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Michael Ellerman <michael@ellerman.id.au>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Victor Kaplansky <VICTORK@il.ibm.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Reviewed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
---
Documentation/memory-barriers.txt | 241 +++++++++++++++++++-------------------
1 file changed, 123 insertions(+), 118 deletions(-)
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -381,39 +381,44 @@ VARIETIES OF MEMORY BARRIER
And a couple of implicit varieties:
- (5) LOCK operations.
+ (5) ACQUIRE operations.
This acts as a one-way permeable barrier. It guarantees that all memory
- operations after the LOCK operation will appear to happen after the LOCK
- operation with respect to the other components of the system.
+ operations after the ACQUIRE operation will appear to happen after the
+ ACQUIRE operation with respect to the other components of the system.
+ ACQUIRE operations include LOCK operations and smp_load_acquire()
+ operations.
- Memory operations that occur before a LOCK operation may appear to happen
- after it completes.
+ Memory operations that occur before an ACQUIRE operation may appear to
+ happen after it completes.
- A LOCK operation should almost always be paired with an UNLOCK operation.
+ An ACQUIRE operation should almost always be paired with a RELEASE
+ operation.
- (6) UNLOCK operations.
+ (6) RELEASE operations.
This also acts as a one-way permeable barrier. It guarantees that all
- memory operations before the UNLOCK operation will appear to happen before
- the UNLOCK operation with respect to the other components of the system.
+ memory operations before the RELEASE operation will appear to happen
+ before the RELEASE operation with respect to the other components of the
+ system. RELEASE operations include UNLOCK operations and
+ smp_store_release() operations.
- Memory operations that occur after an UNLOCK operation may appear to
+ Memory operations that occur after a RELEASE operation may appear to
happen before it completes.
- The use of LOCK and UNLOCK operations generally precludes the need for
- other sorts of memory barrier (but note the exceptions mentioned in the
- subsection "MMIO write barrier"). In addition, an UNLOCK+LOCK pair
- is -not- guaranteed to act as a full memory barrier. However,
- after a LOCK on a given lock variable, all memory accesses preceding any
- prior UNLOCK on that same variable are guaranteed to be visible.
- In other words, within a given lock variable's critical section,
- all accesses of all previous critical sections for that lock variable
- are guaranteed to have completed.
+ The use of ACQUIRE and RELEASE operations generally precludes the need
+ for other sorts of memory barrier (but note the exceptions mentioned in
+ the subsection "MMIO write barrier"). In addition, a RELEASE+ACQUIRE
+ pair is -not- guaranteed to act as a full memory barrier. However, after
+ an ACQUIRE on a given variable, all memory accesses preceding any prior
+ RELEASE on that same variable are guaranteed to be visible. In other
+ words, within a given variable's critical section, all accesses of all
+ previous critical sections for that variable are guaranteed to have
+ completed.
- This means that LOCK acts as a minimal "acquire" operation and
- UNLOCK acts as a minimal "release" operation.
+ This means that ACQUIRE acts as a minimal "acquire" operation and
+ RELEASE acts as a minimal "release" operation.
Memory barriers are only required where there's a possibility of interaction
@@ -1585,7 +1590,7 @@ CPU from reordering them.
clear_bit( ... );
This prevents memory operations before the clear leaking to after it. See
- the subsection on "Locking Functions" with reference to UNLOCK operation
+ the subsection on "Locking Functions" with reference to RELEASE operation
implications.
See Documentation/atomic_ops.txt for more information. See the "Atomic
@@ -1619,8 +1624,8 @@ provide more substantial guarantees, but
of arch specific code.
-LOCKING FUNCTIONS
------------------
+ACQUIRING FUNCTIONS
+-------------------
The Linux kernel has a number of locking constructs:
@@ -1631,106 +1636,106 @@ LOCKING FUNCTIONS
(*) R/W semaphores
(*) RCU
-In all cases there are variants on "LOCK" operations and "UNLOCK" operations
+In all cases there are variants on "ACQUIRE" operations and "RELEASE" operations
for each construct. These operations all imply certain barriers:
- (1) LOCK operation implication:
+ (1) ACQUIRE operation implication:
- Memory operations issued after the LOCK will be completed after the LOCK
- operation has completed.
+ Memory operations issued after the ACQUIRE will be completed after the
+ ACQUIRE operation has completed.
- Memory operations issued before the LOCK may be completed after the
- LOCK operation has completed. An smp_mb__before_spinlock(), combined
- with a following LOCK, orders prior loads against subsequent stores
- and stores and prior stores against subsequent stores. Note that
- this is weaker than smp_mb()! The smp_mb__before_spinlock()
- primitive is free on many architectures.
+ Memory operations issued before the ACQUIRE may be completed after the
+ ACQUIRE operation has completed. An smp_mb__before_spinlock(), combined
+ with a following ACQUIRE, orders prior loads against subsequent stores and
+ stores and prior stores against subsequent stores. Note that this is
+ weaker than smp_mb()! The smp_mb__before_spinlock() primitive is free on
+ many architectures.
- (2) UNLOCK operation implication:
+ (2) RELEASE operation implication:
- Memory operations issued before the UNLOCK will be completed before the
- UNLOCK operation has completed.
+ Memory operations issued before the RELEASE will be completed before the
+ RELEASE operation has completed.
- Memory operations issued after the UNLOCK may be completed before the
- UNLOCK operation has completed.
+ Memory operations issued after the RELEASE may be completed before the
+ RELEASE operation has completed.
- (3) LOCK vs LOCK implication:
+ (3) ACQUIRE vs ACQUIRE implication:
- All LOCK operations issued before another LOCK operation will be completed
- before that LOCK operation.
+ All ACQUIRE operations issued before another ACQUIRE operation will be
+ completed before that ACQUIRE operation.
- (4) LOCK vs UNLOCK implication:
+ (4) ACQUIRE vs RELEASE implication:
- All LOCK operations issued before an UNLOCK operation will be completed
- before the UNLOCK operation.
+ All ACQUIRE operations issued before a RELEASE operation will be
+ completed before the RELEASE operation.
- (5) Failed conditional LOCK implication:
+ (5) Failed conditional ACQUIRE implication:
- Certain variants of the LOCK operation may fail, either due to being
- unable to get the lock immediately, or due to receiving an unblocked
+ Certain locking variants of the ACQUIRE operation may fail, either due to
+ being unable to get the lock immediately, or due to receiving an unblocked
signal whilst asleep waiting for the lock to become available. Failed
locks do not imply any sort of barrier.
-[!] Note: one of the consequences of LOCKs and UNLOCKs being only one-way
- barriers is that the effects of instructions outside of a critical section
- may seep into the inside of the critical section.
-
-A LOCK followed by an UNLOCK may not be assumed to be full memory barrier
-because it is possible for an access preceding the LOCK to happen after the
-LOCK, and an access following the UNLOCK to happen before the UNLOCK, and the
-two accesses can themselves then cross:
+[!] Note: one of the consequences of lock ACQUIREs and RELEASEs being only
+one-way barriers is that the effects of instructions outside of a critical
+section may seep into the inside of the critical section.
+
+An ACQUIRE followed by a RELEASE may not be assumed to be full memory barrier
+because it is possible for an access preceding the ACQUIRE to happen after the
+ACQUIRE, and an access following the RELEASE to happen before the RELEASE, and
+the two accesses can themselves then cross:
*A = a;
- LOCK M
- UNLOCK M
+ ACQUIRE M
+ RELEASE M
*B = b;
may occur as:
- LOCK M, STORE *B, STORE *A, UNLOCK M
+ ACQUIRE M, STORE *B, STORE *A, RELEASE M
-This same reordering can of course occur if the LOCK and UNLOCK are
-to the same lock variable, but only from the perspective of another
-CPU not holding that lock.
-
-In short, an UNLOCK followed by a LOCK may -not- be assumed to be a full
-memory barrier because it is possible for a preceding UNLOCK to pass a
-later LOCK from the viewpoint of the CPU, but not from the viewpoint
+This same reordering can of course occur if the lock's ACQUIRE and RELEASE are
+to the same lock variable, but only from the perspective of another CPU not
+holding that lock.
+
+In short, a RELEASE followed by an ACQUIRE may -not- be assumed to be a full
+memory barrier because it is possible for a preceding RELEASE to pass a
+later ACQUIRE from the viewpoint of the CPU, but not from the viewpoint
of the compiler. Note that deadlocks cannot be introduced by this
-interchange because if such a deadlock threatened, the UNLOCK would
+interchange because if such a deadlock threatened, the RELEASE would
simply complete.
-If it is necessary for an UNLOCK-LOCK pair to produce a full barrier,
-the LOCK can be followed by an smp_mb__after_unlock_lock() invocation.
-This will produce a full barrier if either (a) the UNLOCK and the LOCK
-are executed by the same CPU or task, or (b) the UNLOCK and LOCK act
-on the same lock variable. The smp_mb__after_unlock_lock() primitive
-is free on many architectures. Without smp_mb__after_unlock_lock(),
-the critical sections corresponding to the UNLOCK and the LOCK can cross:
+If it is necessary for a RELEASE-ACQUIRE pair to produce a full barrier, the
+ACQUIRE can be followed by an smp_mb__after_unlock_lock() invocation. This
+will produce a full barrier if either (a) the RELEASE and the ACQUIRE are
+executed by the same CPU or task, or (b) the RELEASE and ACQUIRE act on the
+same variable. The smp_mb__after_unlock_lock() primitive is free on many
+architectures. Without smp_mb__after_unlock_lock(), the critical sections
+corresponding to the RELEASE and the ACQUIRE can cross:
*A = a;
- UNLOCK M
- LOCK N
+ RELEASE M
+ ACQUIRE N
*B = b;
could occur as:
- LOCK N, STORE *B, STORE *A, UNLOCK M
+ ACQUIRE N, STORE *B, STORE *A, RELEASE M
With smp_mb__after_unlock_lock(), they cannot, so that:
*A = a;
- UNLOCK M
- LOCK N
+ RELEASE M
+ ACQUIRE N
smp_mb__after_unlock_lock();
*B = b;
will always occur as either of the following:
- STORE *A, UNLOCK, LOCK, STORE *B
- STORE *A, LOCK, UNLOCK, STORE *B
+ STORE *A, RELEASE, ACQUIRE, STORE *B
+ STORE *A, ACQUIRE, RELEASE, STORE *B
-If the UNLOCK and LOCK were instead both operating on the same lock
+If the RELEASE and ACQUIRE were instead both operating on the same lock
variable, only the first of these two alternatives can occur.
Locks and semaphores may not provide any guarantee of ordering on UP compiled
@@ -1745,33 +1750,33 @@ See also the section on "Inter-CPU locki
*A = a;
*B = b;
- LOCK
+ ACQUIRE
*C = c;
*D = d;
- UNLOCK
+ RELEASE
*E = e;
*F = f;
The following sequence of events is acceptable:
- LOCK, {*F,*A}, *E, {*C,*D}, *B, UNLOCK
+ ACQUIRE, {*F,*A}, *E, {*C,*D}, *B, RELEASE
[+] Note that {*F,*A} indicates a combined access.
But none of the following are:
- {*F,*A}, *B, LOCK, *C, *D, UNLOCK, *E
- *A, *B, *C, LOCK, *D, UNLOCK, *E, *F
- *A, *B, LOCK, *C, UNLOCK, *D, *E, *F
- *B, LOCK, *C, *D, UNLOCK, {*F,*A}, *E
+ {*F,*A}, *B, ACQUIRE, *C, *D, RELEASE, *E
+ *A, *B, *C, ACQUIRE, *D, RELEASE, *E, *F
+ *A, *B, ACQUIRE, *C, RELEASE, *D, *E, *F
+ *B, ACQUIRE, *C, *D, RELEASE, {*F,*A}, *E
INTERRUPT DISABLING FUNCTIONS
-----------------------------
-Functions that disable interrupts (LOCK equivalent) and enable interrupts
-(UNLOCK equivalent) will act as compiler barriers only. So if memory or I/O
+Functions that disable interrupts (ACQUIRE equivalent) and enable interrupts
+(RELEASE equivalent) will act as compiler barriers only. So if memory or I/O
barriers are required in such a situation, they must be provided from some
other means.
@@ -1910,17 +1915,17 @@ MISCELLANEOUS FUNCTIONS
(*) schedule() and similar imply full memory barriers.
-=================================
-INTER-CPU LOCKING BARRIER EFFECTS
-=================================
+===================================
+INTER-CPU ACQUIRING BARRIER EFFECTS
+===================================
On SMP systems locking primitives give a more substantial form of barrier: one
that does affect memory access ordering on other CPUs, within the context of
conflict on any particular lock.
-LOCKS VS MEMORY ACCESSES
-------------------------
+ACQUIRES VS MEMORY ACCESSES
+---------------------------
Consider the following: the system has a pair of spinlocks (M) and (Q), and
three CPUs; then should the following sequence of events occur:
@@ -1928,24 +1933,24 @@ Consider the following: the system has a
CPU 1 CPU 2
=============================== ===============================
ACCESS_ONCE(*A) = a; ACCESS_ONCE(*E) = e;
- LOCK M LOCK Q
+ ACQUIRE M ACQUIRE Q
ACCESS_ONCE(*B) = b; ACCESS_ONCE(*F) = f;
ACCESS_ONCE(*C) = c; ACCESS_ONCE(*G) = g;
- UNLOCK M UNLOCK Q
+ RELEASE M RELEASE Q
ACCESS_ONCE(*D) = d; ACCESS_ONCE(*H) = h;
Then there is no guarantee as to what order CPU 3 will see the accesses to *A
through *H occur in, other than the constraints imposed by the separate locks
on the separate CPUs. It might, for example, see:
- *E, LOCK M, LOCK Q, *G, *C, *F, *A, *B, UNLOCK Q, *D, *H, UNLOCK M
+ *E, ACQUIRE M, ACQUIRE Q, *G, *C, *F, *A, *B, RELEASE Q, *D, *H, RELEASE M
But it won't see any of:
- *B, *C or *D preceding LOCK M
- *A, *B or *C following UNLOCK M
- *F, *G or *H preceding LOCK Q
- *E, *F or *G following UNLOCK Q
+ *B, *C or *D preceding ACQUIRE M
+ *A, *B or *C following RELEASE M
+ *F, *G or *H preceding ACQUIRE Q
+ *E, *F or *G following RELEASE Q
However, if the following occurs:
@@ -1953,29 +1958,29 @@ through *H occur in, other than the cons
CPU 1 CPU 2
=============================== ===============================
ACCESS_ONCE(*A) = a;
- LOCK M [1]
+ ACQUIRE M [1]
ACCESS_ONCE(*B) = b;
ACCESS_ONCE(*C) = c;
- UNLOCK M [1]
+ RELEASE M [1]
ACCESS_ONCE(*D) = d; ACCESS_ONCE(*E) = e;
- LOCK M [2]
+ ACQUIRE M [2]
smp_mb__after_unlock_lock();
ACCESS_ONCE(*F) = f;
ACCESS_ONCE(*G) = g;
- UNLOCK M [2]
+ RELEASE M [2]
ACCESS_ONCE(*H) = h;
CPU 3 might see:
- *E, LOCK M [1], *C, *B, *A, UNLOCK M [1],
- LOCK M [2], *H, *F, *G, UNLOCK M [2], *D
+ *E, ACQUIRE M [1], *C, *B, *A, RELEASE M [1],
+ ACQUIRE M [2], *H, *F, *G, RELEASE M [2], *D
But assuming CPU 1 gets the lock first, CPU 3 won't see any of:
- *B, *C, *D, *F, *G or *H preceding LOCK M [1]
- *A, *B or *C following UNLOCK M [1]
- *F, *G or *H preceding LOCK M [2]
- *A, *B, *C, *E, *F or *G following UNLOCK M [2]
+ *B, *C, *D, *F, *G or *H preceding ACQUIRE M [1]
+ *A, *B or *C following RELEASE M [1]
+ *F, *G or *H preceding ACQUIRE M [2]
+ *A, *B, *C, *E, *F or *G following RELEASE M [2]
Note that the smp_mb__after_unlock_lock() is critically important
here: Without it CPU 3 might see some of the above orderings.
@@ -1983,8 +1988,8 @@ Without smp_mb__after_unlock_lock(), the
to be seen in order unless CPU 3 holds lock M.
-LOCKS VS I/O ACCESSES
----------------------
+ACQUIRES VS I/O ACCESSES
+------------------------
Under certain circumstances (especially involving NUMA), I/O accesses within
two spinlocked sections on two different CPUs may be seen as interleaved by the
@@ -2202,13 +2207,13 @@ about the state (old or new) implies an
/* when succeeds (returns 1) */
atomic_add_unless(); atomic_long_add_unless();
-These are used for such things as implementing LOCK-class and UNLOCK-class
+These are used for such things as implementing ACQUIRE-class and RELEASE-class
operations and adjusting reference counters towards object destruction, and as
such the implicit memory barrier effects are necessary.
The following operations are potential problems as they do _not_ imply memory
-barriers, but might be used for implementing such things as UNLOCK-class
+barriers, but might be used for implementing such things as RELEASE-class
operations:
atomic_set();
@@ -2250,7 +2255,7 @@ barriers are needed or not.
clear_bit_unlock();
__clear_bit_unlock();
-These implement LOCK-class and UNLOCK-class operations. These should be used in
+These implement ACQUIRE-class and RELEASE-class operations. These should be used in
preference to other operations when implementing locking primitives, because
their implementations can be optimised on many architectures.
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCH 2/4] arch: Move smp_mb__{before,after}_atomic_{inc,dec}.h into asm/atomic.h
2013-12-18 19:08 [PATCH 0/4] arch: Introduce smp_load_acquire() and smp_store_release() Peter Zijlstra
2013-12-18 19:08 ` [PATCH 1/4] doc: Rename LOCK/UNLOCK to ACQUIRE/RELEASE Peter Zijlstra
@ 2013-12-18 19:08 ` Peter Zijlstra
2013-12-18 19:08 ` [PATCH 3/4] arch: Clean up asm/barrier.h implementations using asm-generic/barrier.h Peter Zijlstra
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: Peter Zijlstra @ 2013-12-18 19:08 UTC (permalink / raw)
To: linux-arch, linux-kernel
Cc: geert, paulmck, torvalds, VICTORK, oleg, anton, benh, fweisbec,
mathieu.desnoyers, michael, mikey, linux, schwidefsky,
heiko.carstens, tony.luck, Peter Zijlstra
[-- Attachment #1: peterz-arch-move-atomic-barriers.patch --]
[-- Type: text/plain, Size: 2490 bytes --]
Move the barriers functions that depend on the atomic implementation
into the atomic implementation.
Acked-by: Vineet Gupta <vgupta@synopsys.com> [for arch/arc bits]
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
---
arch/arc/include/asm/atomic.h | 5 +++++
arch/arc/include/asm/barrier.h | 5 -----
arch/hexagon/include/asm/atomic.h | 6 +++++-
arch/hexagon/include/asm/barrier.h | 4 ----
4 files changed, 10 insertions(+), 10 deletions(-)
--- a/arch/arc/include/asm/atomic.h
+++ b/arch/arc/include/asm/atomic.h
@@ -190,6 +190,11 @@ static inline void atomic_clear_mask(uns
#endif /* !CONFIG_ARC_HAS_LLSC */
+#define smp_mb__before_atomic_dec() barrier()
+#define smp_mb__after_atomic_dec() barrier()
+#define smp_mb__before_atomic_inc() barrier()
+#define smp_mb__after_atomic_inc() barrier()
+
/**
* __atomic_add_unless - add unless the number is a given value
* @v: pointer of type atomic_t
--- a/arch/arc/include/asm/barrier.h
+++ b/arch/arc/include/asm/barrier.h
@@ -30,11 +30,6 @@
#define smp_wmb() barrier()
#endif
-#define smp_mb__before_atomic_dec() barrier()
-#define smp_mb__after_atomic_dec() barrier()
-#define smp_mb__before_atomic_inc() barrier()
-#define smp_mb__after_atomic_inc() barrier()
-
#define smp_read_barrier_depends() do { } while (0)
#endif
--- a/arch/hexagon/include/asm/atomic.h
+++ b/arch/hexagon/include/asm/atomic.h
@@ -160,8 +160,12 @@ static inline int __atomic_add_unless(at
#define atomic_sub_and_test(i, v) (atomic_sub_return(i, (v)) == 0)
#define atomic_add_negative(i, v) (atomic_add_return(i, (v)) < 0)
-
#define atomic_inc_return(v) (atomic_add_return(1, v))
#define atomic_dec_return(v) (atomic_sub_return(1, v))
+#define smp_mb__before_atomic_dec() barrier()
+#define smp_mb__after_atomic_dec() barrier()
+#define smp_mb__before_atomic_inc() barrier()
+#define smp_mb__after_atomic_inc() barrier()
+
#endif
--- a/arch/hexagon/include/asm/barrier.h
+++ b/arch/hexagon/include/asm/barrier.h
@@ -29,10 +29,6 @@
#define smp_read_barrier_depends() barrier()
#define smp_wmb() barrier()
#define smp_mb() barrier()
-#define smp_mb__before_atomic_dec() barrier()
-#define smp_mb__after_atomic_dec() barrier()
-#define smp_mb__before_atomic_inc() barrier()
-#define smp_mb__after_atomic_inc() barrier()
/* Set a value and use a memory barrier. Used by the scheduler somewhere. */
#define set_mb(var, value) \
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCH 3/4] arch: Clean up asm/barrier.h implementations using asm-generic/barrier.h
2013-12-18 19:08 [PATCH 0/4] arch: Introduce smp_load_acquire() and smp_store_release() Peter Zijlstra
2013-12-18 19:08 ` [PATCH 1/4] doc: Rename LOCK/UNLOCK to ACQUIRE/RELEASE Peter Zijlstra
2013-12-18 19:08 ` [PATCH 2/4] arch: Move smp_mb__{before,after}_atomic_{inc,dec}.h into asm/atomic.h Peter Zijlstra
@ 2013-12-18 19:08 ` Peter Zijlstra
2013-12-18 19:08 ` [PATCH 4/4] arch: Introduce smp_load_acquire(), smp_store_release() Peter Zijlstra
2013-12-18 20:55 ` [PATCH 0/4] arch: Introduce smp_load_acquire() and smp_store_release() Paul E. McKenney
4 siblings, 0 replies; 6+ messages in thread
From: Peter Zijlstra @ 2013-12-18 19:08 UTC (permalink / raw)
To: linux-arch, linux-kernel
Cc: geert, paulmck, torvalds, VICTORK, oleg, anton, benh, fweisbec,
mathieu.desnoyers, michael, mikey, linux, schwidefsky,
heiko.carstens, tony.luck, Peter Zijlstra
[-- Attachment #1: peter_zijlstra-arch-generic-barrier.patch --]
[-- Type: text/plain, Size: 23974 bytes --]
We're going to be adding a few new barrier primitives, and in order to
avoid endless duplication make more agressive use of
asm-generic/barrier.h.
Change the asm-generic/barrier.h such that it allows partial barrier
definitions and fills out the rest with defaults.
There are a few architectures (m32r, m68k) that could probably
do away with their barrier.h file entirely but are kept for now due to
their unconventional nop() implementation.
Cc: Michael Ellerman <michael@ellerman.id.au>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Victor Kaplansky <VICTORK@il.ibm.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Suggested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Reviewed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
---
arch/alpha/include/asm/barrier.h | 25 ++--------
arch/arc/include/asm/Kbuild | 1
arch/avr32/include/asm/barrier.h | 17 ++-----
arch/blackfin/include/asm/barrier.h | 18 -------
arch/cris/include/asm/Kbuild | 1
arch/cris/include/asm/barrier.h | 25 ----------
arch/frv/include/asm/barrier.h | 8 ---
arch/hexagon/include/asm/Kbuild | 1
arch/m32r/include/asm/barrier.h | 80 ----------------------------------
arch/m68k/include/asm/barrier.h | 14 -----
arch/microblaze/include/asm/Kbuild | 1
arch/microblaze/include/asm/barrier.h | 27 -----------
arch/mn10300/include/asm/Kbuild | 1
arch/mn10300/include/asm/barrier.h | 37 ---------------
arch/parisc/include/asm/Kbuild | 1
arch/parisc/include/asm/barrier.h | 35 --------------
arch/score/include/asm/Kbuild | 1
arch/score/include/asm/barrier.h | 16 ------
arch/sh/include/asm/barrier.h | 21 +-------
arch/sparc/include/asm/barrier_32.h | 12 -----
arch/tile/include/asm/barrier.h | 68 ----------------------------
arch/unicore32/include/asm/barrier.h | 11 ----
arch/xtensa/include/asm/barrier.h | 9 ---
include/asm-generic/barrier.h | 42 ++++++++++++-----
24 files changed, 58 insertions(+), 414 deletions(-)
--- a/arch/alpha/include/asm/barrier.h
+++ b/arch/alpha/include/asm/barrier.h
@@ -3,33 +3,18 @@
#include <asm/compiler.h>
-#define mb() \
-__asm__ __volatile__("mb": : :"memory")
+#define mb() __asm__ __volatile__("mb": : :"memory")
+#define rmb() __asm__ __volatile__("mb": : :"memory")
+#define wmb() __asm__ __volatile__("wmb": : :"memory")
-#define rmb() \
-__asm__ __volatile__("mb": : :"memory")
-
-#define wmb() \
-__asm__ __volatile__("wmb": : :"memory")
-
-#define read_barrier_depends() \
-__asm__ __volatile__("mb": : :"memory")
+#define read_barrier_depends() __asm__ __volatile__("mb": : :"memory")
#ifdef CONFIG_SMP
#define __ASM_SMP_MB "\tmb\n"
-#define smp_mb() mb()
-#define smp_rmb() rmb()
-#define smp_wmb() wmb()
-#define smp_read_barrier_depends() read_barrier_depends()
#else
#define __ASM_SMP_MB
-#define smp_mb() barrier()
-#define smp_rmb() barrier()
-#define smp_wmb() barrier()
-#define smp_read_barrier_depends() do { } while (0)
#endif
-#define set_mb(var, value) \
-do { var = value; mb(); } while (0)
+#include <asm-generic/barrier.h>
#endif /* __BARRIER_H */
--- a/arch/arc/include/asm/Kbuild
+++ b/arch/arc/include/asm/Kbuild
@@ -47,3 +47,4 @@ generic-y += user.h
generic-y += vga.h
generic-y += xor.h
generic-y += preempt.h
+generic-y += barrier.h
--- a/arch/avr32/include/asm/barrier.h
+++ b/arch/avr32/include/asm/barrier.h
@@ -8,22 +8,15 @@
#ifndef __ASM_AVR32_BARRIER_H
#define __ASM_AVR32_BARRIER_H
-#define nop() asm volatile("nop")
-
-#define mb() asm volatile("" : : : "memory")
-#define rmb() mb()
-#define wmb() asm volatile("sync 0" : : : "memory")
-#define read_barrier_depends() do { } while(0)
-#define set_mb(var, value) do { var = value; mb(); } while(0)
+/*
+ * Weirdest thing ever.. no full barrier, but it has a write barrier!
+ */
+#define wmb() asm volatile("sync 0" : : : "memory")
#ifdef CONFIG_SMP
# error "The AVR32 port does not support SMP"
-#else
-# define smp_mb() barrier()
-# define smp_rmb() barrier()
-# define smp_wmb() barrier()
-# define smp_read_barrier_depends() do { } while(0)
#endif
+#include <asm-generic/barrier.h>
#endif /* __ASM_AVR32_BARRIER_H */
--- a/arch/blackfin/include/asm/barrier.h
+++ b/arch/blackfin/include/asm/barrier.h
@@ -23,26 +23,10 @@
# define rmb() do { barrier(); smp_check_barrier(); } while (0)
# define wmb() do { barrier(); smp_mark_barrier(); } while (0)
# define read_barrier_depends() do { barrier(); smp_check_barrier(); } while (0)
-#else
-# define mb() barrier()
-# define rmb() barrier()
-# define wmb() barrier()
-# define read_barrier_depends() do { } while (0)
#endif
-#else /* !CONFIG_SMP */
-
-#define mb() barrier()
-#define rmb() barrier()
-#define wmb() barrier()
-#define read_barrier_depends() do { } while (0)
-
#endif /* !CONFIG_SMP */
-#define smp_mb() mb()
-#define smp_rmb() rmb()
-#define smp_wmb() wmb()
-#define set_mb(var, value) do { var = value; mb(); } while (0)
-#define smp_read_barrier_depends() read_barrier_depends()
+#include <asm-generic/barrier.h>
#endif /* _BLACKFIN_BARRIER_H */
--- a/arch/cris/include/asm/Kbuild
+++ b/arch/cris/include/asm/Kbuild
@@ -12,3 +12,4 @@ generic-y += trace_clock.h
generic-y += vga.h
generic-y += xor.h
generic-y += preempt.h
+generic-y += barrier.h
--- a/arch/cris/include/asm/barrier.h
+++ /dev/null
@@ -1,25 +0,0 @@
-#ifndef __ASM_CRIS_BARRIER_H
-#define __ASM_CRIS_BARRIER_H
-
-#define nop() __asm__ __volatile__ ("nop");
-
-#define barrier() __asm__ __volatile__("": : :"memory")
-#define mb() barrier()
-#define rmb() mb()
-#define wmb() mb()
-#define read_barrier_depends() do { } while(0)
-#define set_mb(var, value) do { var = value; mb(); } while (0)
-
-#ifdef CONFIG_SMP
-#define smp_mb() mb()
-#define smp_rmb() rmb()
-#define smp_wmb() wmb()
-#define smp_read_barrier_depends() read_barrier_depends()
-#else
-#define smp_mb() barrier()
-#define smp_rmb() barrier()
-#define smp_wmb() barrier()
-#define smp_read_barrier_depends() do { } while(0)
-#endif
-
-#endif /* __ASM_CRIS_BARRIER_H */
--- a/arch/frv/include/asm/barrier.h
+++ b/arch/frv/include/asm/barrier.h
@@ -17,13 +17,7 @@
#define mb() asm volatile ("membar" : : :"memory")
#define rmb() asm volatile ("membar" : : :"memory")
#define wmb() asm volatile ("membar" : : :"memory")
-#define read_barrier_depends() do { } while (0)
-#define smp_mb() barrier()
-#define smp_rmb() barrier()
-#define smp_wmb() barrier()
-#define smp_read_barrier_depends() do {} while(0)
-#define set_mb(var, value) \
- do { var = (value); barrier(); } while (0)
+#include <asm-generic/barrier.h>
#endif /* _ASM_BARRIER_H */
--- a/arch/hexagon/include/asm/Kbuild
+++ b/arch/hexagon/include/asm/Kbuild
@@ -54,3 +54,4 @@ generic-y += ucontext.h
generic-y += unaligned.h
generic-y += xor.h
generic-y += preempt.h
+generic-y += barrier.h
--- a/arch/m32r/include/asm/barrier.h
+++ b/arch/m32r/include/asm/barrier.h
@@ -11,84 +11,6 @@
#define nop() __asm__ __volatile__ ("nop" : : )
-/*
- * Memory barrier.
- *
- * mb() prevents loads and stores being reordered across this point.
- * rmb() prevents loads being reordered across this point.
- * wmb() prevents stores being reordered across this point.
- */
-#define mb() barrier()
-#define rmb() mb()
-#define wmb() mb()
-
-/**
- * read_barrier_depends - Flush all pending reads that subsequents reads
- * depend on.
- *
- * No data-dependent reads from memory-like regions are ever reordered
- * over this barrier. All reads preceding this primitive are guaranteed
- * to access memory (but not necessarily other CPUs' caches) before any
- * reads following this primitive that depend on the data return by
- * any of the preceding reads. This primitive is much lighter weight than
- * rmb() on most CPUs, and is never heavier weight than is
- * rmb().
- *
- * These ordering constraints are respected by both the local CPU
- * and the compiler.
- *
- * Ordering is not guaranteed by anything other than these primitives,
- * not even by data dependencies. See the documentation for
- * memory_barrier() for examples and URLs to more information.
- *
- * For example, the following code would force ordering (the initial
- * value of "a" is zero, "b" is one, and "p" is "&a"):
- *
- * <programlisting>
- * CPU 0 CPU 1
- *
- * b = 2;
- * memory_barrier();
- * p = &b; q = p;
- * read_barrier_depends();
- * d = *q;
- * </programlisting>
- *
- *
- * because the read of "*q" depends on the read of "p" and these
- * two reads are separated by a read_barrier_depends(). However,
- * the following code, with the same initial values for "a" and "b":
- *
- * <programlisting>
- * CPU 0 CPU 1
- *
- * a = 2;
- * memory_barrier();
- * b = 3; y = b;
- * read_barrier_depends();
- * x = a;
- * </programlisting>
- *
- * does not enforce ordering, since there is no data dependency between
- * the read of "a" and the read of "b". Therefore, on some CPUs, such
- * as Alpha, "y" could be set to 3 and "x" to 0. Use rmb()
- * in cases like this where there are no data dependencies.
- **/
-
-#define read_barrier_depends() do { } while (0)
-
-#ifdef CONFIG_SMP
-#define smp_mb() mb()
-#define smp_rmb() rmb()
-#define smp_wmb() wmb()
-#define smp_read_barrier_depends() read_barrier_depends()
-#define set_mb(var, value) do { (void) xchg(&var, value); } while (0)
-#else
-#define smp_mb() barrier()
-#define smp_rmb() barrier()
-#define smp_wmb() barrier()
-#define smp_read_barrier_depends() do { } while (0)
-#define set_mb(var, value) do { var = value; barrier(); } while (0)
-#endif
+#include <asm-generic/barrier.h>
#endif /* _ASM_M32R_BARRIER_H */
--- a/arch/m68k/include/asm/barrier.h
+++ b/arch/m68k/include/asm/barrier.h
@@ -1,20 +1,8 @@
#ifndef _M68K_BARRIER_H
#define _M68K_BARRIER_H
-/*
- * Force strict CPU ordering.
- * Not really required on m68k...
- */
#define nop() do { asm volatile ("nop"); barrier(); } while (0)
-#define mb() barrier()
-#define rmb() barrier()
-#define wmb() barrier()
-#define read_barrier_depends() ((void)0)
-#define set_mb(var, value) ({ (var) = (value); wmb(); })
-#define smp_mb() barrier()
-#define smp_rmb() barrier()
-#define smp_wmb() barrier()
-#define smp_read_barrier_depends() ((void)0)
+#include <asm-generic/barrier.h>
#endif /* _M68K_BARRIER_H */
--- a/arch/microblaze/include/asm/Kbuild
+++ b/arch/microblaze/include/asm/Kbuild
@@ -4,3 +4,4 @@ generic-y += exec.h
generic-y += trace_clock.h
generic-y += syscalls.h
generic-y += preempt.h
+generic-y += barrier.h
--- a/arch/microblaze/include/asm/barrier.h
+++ /dev/null
@@ -1,27 +0,0 @@
-/*
- * Copyright (C) 2006 Atmark Techno, Inc.
- *
- * This file is subject to the terms and conditions of the GNU General Public
- * License. See the file "COPYING" in the main directory of this archive
- * for more details.
- */
-
-#ifndef _ASM_MICROBLAZE_BARRIER_H
-#define _ASM_MICROBLAZE_BARRIER_H
-
-#define nop() asm volatile ("nop")
-
-#define smp_read_barrier_depends() do {} while (0)
-#define read_barrier_depends() do {} while (0)
-
-#define mb() barrier()
-#define rmb() mb()
-#define wmb() mb()
-#define set_mb(var, value) do { var = value; mb(); } while (0)
-#define set_wmb(var, value) do { var = value; wmb(); } while (0)
-
-#define smp_mb() mb()
-#define smp_rmb() rmb()
-#define smp_wmb() wmb()
-
-#endif /* _ASM_MICROBLAZE_BARRIER_H */
--- a/arch/mn10300/include/asm/Kbuild
+++ b/arch/mn10300/include/asm/Kbuild
@@ -3,3 +3,4 @@ generic-y += clkdev.h
generic-y += exec.h
generic-y += trace_clock.h
generic-y += preempt.h
+generic-y += barrier.h
--- a/arch/mn10300/include/asm/barrier.h
+++ /dev/null
@@ -1,37 +0,0 @@
-/* MN10300 memory barrier definitions
- *
- * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
- * Written by David Howells (dhowells@redhat.com)
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public Licence
- * as published by the Free Software Foundation; either version
- * 2 of the Licence, or (at your option) any later version.
- */
-#ifndef _ASM_BARRIER_H
-#define _ASM_BARRIER_H
-
-#define nop() asm volatile ("nop")
-
-#define mb() asm volatile ("": : :"memory")
-#define rmb() mb()
-#define wmb() asm volatile ("": : :"memory")
-
-#ifdef CONFIG_SMP
-#define smp_mb() mb()
-#define smp_rmb() rmb()
-#define smp_wmb() wmb()
-#define set_mb(var, value) do { xchg(&var, value); } while (0)
-#else /* CONFIG_SMP */
-#define smp_mb() barrier()
-#define smp_rmb() barrier()
-#define smp_wmb() barrier()
-#define set_mb(var, value) do { var = value; mb(); } while (0)
-#endif /* CONFIG_SMP */
-
-#define set_wmb(var, value) do { var = value; wmb(); } while (0)
-
-#define read_barrier_depends() do {} while (0)
-#define smp_read_barrier_depends() do {} while (0)
-
-#endif /* _ASM_BARRIER_H */
--- a/arch/parisc/include/asm/Kbuild
+++ b/arch/parisc/include/asm/Kbuild
@@ -5,3 +5,4 @@ generic-y += word-at-a-time.h auxvec.h u
poll.h xor.h clkdev.h exec.h
generic-y += trace_clock.h
generic-y += preempt.h
+generic-y += barrier.h
--- a/arch/parisc/include/asm/barrier.h
+++ /dev/null
@@ -1,35 +0,0 @@
-#ifndef __PARISC_BARRIER_H
-#define __PARISC_BARRIER_H
-
-/*
-** This is simply the barrier() macro from linux/kernel.h but when serial.c
-** uses tqueue.h uses smp_mb() defined using barrier(), linux/kernel.h
-** hasn't yet been included yet so it fails, thus repeating the macro here.
-**
-** PA-RISC architecture allows for weakly ordered memory accesses although
-** none of the processors use it. There is a strong ordered bit that is
-** set in the O-bit of the page directory entry. Operating systems that
-** can not tolerate out of order accesses should set this bit when mapping
-** pages. The O-bit of the PSW should also be set to 1 (I don't believe any
-** of the processor implemented the PSW O-bit). The PCX-W ERS states that
-** the TLB O-bit is not implemented so the page directory does not need to
-** have the O-bit set when mapping pages (section 3.1). This section also
-** states that the PSW Y, Z, G, and O bits are not implemented.
-** So it looks like nothing needs to be done for parisc-linux (yet).
-** (thanks to chada for the above comment -ggg)
-**
-** The __asm__ op below simple prevents gcc/ld from reordering
-** instructions across the mb() "call".
-*/
-#define mb() __asm__ __volatile__("":::"memory") /* barrier() */
-#define rmb() mb()
-#define wmb() mb()
-#define smp_mb() mb()
-#define smp_rmb() mb()
-#define smp_wmb() mb()
-#define smp_read_barrier_depends() do { } while(0)
-#define read_barrier_depends() do { } while(0)
-
-#define set_mb(var, value) do { var = value; mb(); } while (0)
-
-#endif /* __PARISC_BARRIER_H */
--- a/arch/score/include/asm/Kbuild
+++ b/arch/score/include/asm/Kbuild
@@ -5,3 +5,4 @@ generic-y += clkdev.h
generic-y += trace_clock.h
generic-y += xor.h
generic-y += preempt.h
+generic-y += barrier.h
--- a/arch/score/include/asm/barrier.h
+++ /dev/null
@@ -1,16 +0,0 @@
-#ifndef _ASM_SCORE_BARRIER_H
-#define _ASM_SCORE_BARRIER_H
-
-#define mb() barrier()
-#define rmb() barrier()
-#define wmb() barrier()
-#define smp_mb() barrier()
-#define smp_rmb() barrier()
-#define smp_wmb() barrier()
-
-#define read_barrier_depends() do {} while (0)
-#define smp_read_barrier_depends() do {} while (0)
-
-#define set_mb(var, value) do {var = value; wmb(); } while (0)
-
-#endif /* _ASM_SCORE_BARRIER_H */
--- a/arch/sh/include/asm/barrier.h
+++ b/arch/sh/include/asm/barrier.h
@@ -26,29 +26,14 @@
#if defined(CONFIG_CPU_SH4A) || defined(CONFIG_CPU_SH5)
#define mb() __asm__ __volatile__ ("synco": : :"memory")
#define rmb() mb()
-#define wmb() __asm__ __volatile__ ("synco": : :"memory")
+#define wmb() mb()
#define ctrl_barrier() __icbi(PAGE_OFFSET)
-#define read_barrier_depends() do { } while(0)
#else
-#define mb() __asm__ __volatile__ ("": : :"memory")
-#define rmb() mb()
-#define wmb() __asm__ __volatile__ ("": : :"memory")
#define ctrl_barrier() __asm__ __volatile__ ("nop;nop;nop;nop;nop;nop;nop;nop")
-#define read_barrier_depends() do { } while(0)
-#endif
-
-#ifdef CONFIG_SMP
-#define smp_mb() mb()
-#define smp_rmb() rmb()
-#define smp_wmb() wmb()
-#define smp_read_barrier_depends() read_barrier_depends()
-#else
-#define smp_mb() barrier()
-#define smp_rmb() barrier()
-#define smp_wmb() barrier()
-#define smp_read_barrier_depends() do { } while(0)
#endif
#define set_mb(var, value) do { (void)xchg(&var, value); } while (0)
+#include <asm-generic/barrier.h>
+
#endif /* __ASM_SH_BARRIER_H */
--- a/arch/sparc/include/asm/barrier_32.h
+++ b/arch/sparc/include/asm/barrier_32.h
@@ -1,15 +1,7 @@
#ifndef __SPARC_BARRIER_H
#define __SPARC_BARRIER_H
-/* XXX Change this if we ever use a PSO mode kernel. */
-#define mb() __asm__ __volatile__ ("" : : : "memory")
-#define rmb() mb()
-#define wmb() mb()
-#define read_barrier_depends() do { } while(0)
-#define set_mb(__var, __value) do { __var = __value; mb(); } while(0)
-#define smp_mb() __asm__ __volatile__("":::"memory")
-#define smp_rmb() __asm__ __volatile__("":::"memory")
-#define smp_wmb() __asm__ __volatile__("":::"memory")
-#define smp_read_barrier_depends() do { } while(0)
+#include <asm/processor.h> /* for nop() */
+#include <asm-generic/barrier.h>
#endif /* !(__SPARC_BARRIER_H) */
--- a/arch/tile/include/asm/barrier.h
+++ b/arch/tile/include/asm/barrier.h
@@ -22,59 +22,6 @@
#include <arch/spr_def.h>
#include <asm/timex.h>
-/*
- * read_barrier_depends - Flush all pending reads that subsequents reads
- * depend on.
- *
- * No data-dependent reads from memory-like regions are ever reordered
- * over this barrier. All reads preceding this primitive are guaranteed
- * to access memory (but not necessarily other CPUs' caches) before any
- * reads following this primitive that depend on the data return by
- * any of the preceding reads. This primitive is much lighter weight than
- * rmb() on most CPUs, and is never heavier weight than is
- * rmb().
- *
- * These ordering constraints are respected by both the local CPU
- * and the compiler.
- *
- * Ordering is not guaranteed by anything other than these primitives,
- * not even by data dependencies. See the documentation for
- * memory_barrier() for examples and URLs to more information.
- *
- * For example, the following code would force ordering (the initial
- * value of "a" is zero, "b" is one, and "p" is "&a"):
- *
- * <programlisting>
- * CPU 0 CPU 1
- *
- * b = 2;
- * memory_barrier();
- * p = &b; q = p;
- * read_barrier_depends();
- * d = *q;
- * </programlisting>
- *
- * because the read of "*q" depends on the read of "p" and these
- * two reads are separated by a read_barrier_depends(). However,
- * the following code, with the same initial values for "a" and "b":
- *
- * <programlisting>
- * CPU 0 CPU 1
- *
- * a = 2;
- * memory_barrier();
- * b = 3; y = b;
- * read_barrier_depends();
- * x = a;
- * </programlisting>
- *
- * does not enforce ordering, since there is no data dependency between
- * the read of "a" and the read of "b". Therefore, on some CPUs, such
- * as Alpha, "y" could be set to 3 and "x" to 0. Use rmb()
- * in cases like this where there are no data dependencies.
- */
-#define read_barrier_depends() do { } while (0)
-
#define __sync() __insn_mf()
#include <hv/syscall_public.h>
@@ -125,20 +72,7 @@ mb_incoherent(void)
#define mb() fast_mb()
#define iob() fast_iob()
-#ifdef CONFIG_SMP
-#define smp_mb() mb()
-#define smp_rmb() rmb()
-#define smp_wmb() wmb()
-#define smp_read_barrier_depends() read_barrier_depends()
-#else
-#define smp_mb() barrier()
-#define smp_rmb() barrier()
-#define smp_wmb() barrier()
-#define smp_read_barrier_depends() do { } while (0)
-#endif
-
-#define set_mb(var, value) \
- do { var = value; mb(); } while (0)
+#include <asm-generic/barrier.h>
#endif /* !__ASSEMBLY__ */
#endif /* _ASM_TILE_BARRIER_H */
--- a/arch/unicore32/include/asm/barrier.h
+++ b/arch/unicore32/include/asm/barrier.h
@@ -14,15 +14,6 @@
#define dsb() __asm__ __volatile__ ("" : : : "memory")
#define dmb() __asm__ __volatile__ ("" : : : "memory")
-#define mb() barrier()
-#define rmb() barrier()
-#define wmb() barrier()
-#define smp_mb() barrier()
-#define smp_rmb() barrier()
-#define smp_wmb() barrier()
-#define read_barrier_depends() do { } while (0)
-#define smp_read_barrier_depends() do { } while (0)
-
-#define set_mb(var, value) do { var = value; smp_mb(); } while (0)
+#include <asm-generic/barrier.h>
#endif /* __UNICORE_BARRIER_H__ */
--- a/arch/xtensa/include/asm/barrier.h
+++ b/arch/xtensa/include/asm/barrier.h
@@ -9,21 +9,14 @@
#ifndef _XTENSA_SYSTEM_H
#define _XTENSA_SYSTEM_H
-#define smp_read_barrier_depends() do { } while(0)
-#define read_barrier_depends() do { } while(0)
-
#define mb() ({ __asm__ __volatile__("memw" : : : "memory"); })
#define rmb() barrier()
#define wmb() mb()
#ifdef CONFIG_SMP
#error smp_* not defined
-#else
-#define smp_mb() barrier()
-#define smp_rmb() barrier()
-#define smp_wmb() barrier()
#endif
-#define set_mb(var, value) do { var = value; mb(); } while (0)
+#include <asm-generic/barrier.h>
#endif /* _XTENSA_SYSTEM_H */
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -1,4 +1,5 @@
-/* Generic barrier definitions, based on MN10300 definitions.
+/*
+ * Generic barrier definitions, originally based on MN10300 definitions.
*
* It should be possible to use these on really simple architectures,
* but it serves more as a starting point for new ports.
@@ -16,35 +17,50 @@
#ifndef __ASSEMBLY__
-#define nop() asm volatile ("nop")
+#include <linux/compiler.h>
+
+#ifndef nop
+#define nop() asm volatile ("nop")
+#endif
/*
- * Force strict CPU ordering.
- * And yes, this is required on UP too when we're talking
- * to devices.
+ * Force strict CPU ordering. And yes, this is required on UP too when we're
+ * talking to devices.
*
- * This implementation only contains a compiler barrier.
+ * Fall back to compiler barriers if nothing better is provided.
*/
-#define mb() asm volatile ("": : :"memory")
+#ifndef mb
+#define mb() barrier()
+#endif
+
+#ifndef rmb
#define rmb() mb()
-#define wmb() asm volatile ("": : :"memory")
+#endif
+
+#ifndef wmb
+#define wmb() mb()
+#endif
+
+#ifndef read_barrier_depends
+#define read_barrier_depends() do { } while (0)
+#endif
#ifdef CONFIG_SMP
#define smp_mb() mb()
#define smp_rmb() rmb()
#define smp_wmb() wmb()
+#define smp_read_barrier_depends() read_barrier_depends()
#else
#define smp_mb() barrier()
#define smp_rmb() barrier()
#define smp_wmb() barrier()
+#define smp_read_barrier_depends() do { } while (0)
#endif
-#define set_mb(var, value) do { var = value; mb(); } while (0)
-#define set_wmb(var, value) do { var = value; wmb(); } while (0)
-
-#define read_barrier_depends() do {} while (0)
-#define smp_read_barrier_depends() do {} while (0)
+#ifndef set_mb
+#define set_mb(var, value) do { (var) = (value); mb(); } while (0)
+#endif
#endif /* !__ASSEMBLY__ */
#endif /* __ASM_GENERIC_BARRIER_H */
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCH 4/4] arch: Introduce smp_load_acquire(), smp_store_release()
2013-12-18 19:08 [PATCH 0/4] arch: Introduce smp_load_acquire() and smp_store_release() Peter Zijlstra
` (2 preceding siblings ...)
2013-12-18 19:08 ` [PATCH 3/4] arch: Clean up asm/barrier.h implementations using asm-generic/barrier.h Peter Zijlstra
@ 2013-12-18 19:08 ` Peter Zijlstra
2013-12-18 20:55 ` [PATCH 0/4] arch: Introduce smp_load_acquire() and smp_store_release() Paul E. McKenney
4 siblings, 0 replies; 6+ messages in thread
From: Peter Zijlstra @ 2013-12-18 19:08 UTC (permalink / raw)
To: linux-arch, linux-kernel
Cc: geert, paulmck, torvalds, VICTORK, oleg, anton, benh, fweisbec,
mathieu.desnoyers, michael, mikey, linux, schwidefsky,
heiko.carstens, tony.luck, Peter Zijlstra, Will Deacon
[-- Attachment #1: peter_zijlstra-arch-sr-la.patch --]
[-- Type: text/plain, Size: 12359 bytes --]
A number of situations currently require the heavyweight smp_mb(),
even though there is no need to order prior stores against later
loads. Many architectures have much cheaper ways to handle these
situations, but the Linux kernel currently has no portable way
to make use of them.
This commit therefore supplies smp_load_acquire() and
smp_store_release() to remedy this situation. The new
smp_load_acquire() primitive orders the specified load against
any subsequent reads or writes, while the new smp_store_release()
primitive orders the specifed store against any prior reads or
writes. These primitives allow array-based circular FIFOs to be
implemented without an smp_mb(), and also allow a theoretical
hole in rcu_assign_pointer() to be closed at no additional
expense on most architectures.
In addition, the RCU experience transitioning from explicit
smp_read_barrier_depends() and smp_wmb() to rcu_dereference()
and rcu_assign_pointer(), respectively resulted in substantial
improvements in readability. It therefore seems likely that
replacing other explicit barriers with smp_load_acquire() and
smp_store_release() will provide similar benefits. It appears
that roughly half of the explicit barriers in core kernel code
might be so replaced.
[Changelog by PaulMck]
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Michael Ellerman <michael@ellerman.id.au>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Victor Kaplansky <VICTORK@il.ibm.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Reviewed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
---
arch/arm/include/asm/barrier.h | 15 ++++++++++
arch/arm64/include/asm/barrier.h | 50 ++++++++++++++++++++++++++++++++++++
arch/ia64/include/asm/barrier.h | 23 ++++++++++++++++
arch/metag/include/asm/barrier.h | 15 ++++++++++
arch/mips/include/asm/barrier.h | 15 ++++++++++
arch/powerpc/include/asm/barrier.h | 21 ++++++++++++++-
arch/s390/include/asm/barrier.h | 15 ++++++++++
arch/sparc/include/asm/barrier_64.h | 15 ++++++++++
arch/x86/include/asm/barrier.h | 43 ++++++++++++++++++++++++++++++
include/asm-generic/barrier.h | 15 ++++++++++
include/linux/compiler.h | 9 ++++++
11 files changed, 234 insertions(+), 2 deletions(-)
--- a/arch/arm/include/asm/barrier.h
+++ b/arch/arm/include/asm/barrier.h
@@ -59,6 +59,21 @@
#define smp_wmb() dmb(ishst)
#endif
+#define smp_store_release(p, v) \
+do { \
+ compiletime_assert_atomic_type(*p); \
+ smp_mb(); \
+ ACCESS_ONCE(*p) = (v); \
+} while (0)
+
+#define smp_load_acquire(p) \
+({ \
+ typeof(*p) ___p1 = ACCESS_ONCE(*p); \
+ compiletime_assert_atomic_type(*p); \
+ smp_mb(); \
+ ___p1; \
+})
+
#define read_barrier_depends() do { } while(0)
#define smp_read_barrier_depends() do { } while(0)
--- a/arch/arm64/include/asm/barrier.h
+++ b/arch/arm64/include/asm/barrier.h
@@ -35,10 +35,60 @@
#define smp_mb() barrier()
#define smp_rmb() barrier()
#define smp_wmb() barrier()
+
+#define smp_store_release(p, v) \
+do { \
+ compiletime_assert_atomic_type(*p); \
+ smp_mb(); \
+ ACCESS_ONCE(*p) = (v); \
+} while (0)
+
+#define smp_load_acquire(p) \
+({ \
+ typeof(*p) ___p1 = ACCESS_ONCE(*p); \
+ compiletime_assert_atomic_type(*p); \
+ smp_mb(); \
+ ___p1; \
+})
+
#else
+
#define smp_mb() asm volatile("dmb ish" : : : "memory")
#define smp_rmb() asm volatile("dmb ishld" : : : "memory")
#define smp_wmb() asm volatile("dmb ishst" : : : "memory")
+
+#define smp_store_release(p, v) \
+do { \
+ compiletime_assert_atomic_type(*p); \
+ switch (sizeof(*p)) { \
+ case 4: \
+ asm volatile ("stlr %w1, %0" \
+ : "=Q" (*p) : "r" (v) : "memory"); \
+ break; \
+ case 8: \
+ asm volatile ("stlr %1, %0" \
+ : "=Q" (*p) : "r" (v) : "memory"); \
+ break; \
+ } \
+} while (0)
+
+#define smp_load_acquire(p) \
+({ \
+ typeof(*p) ___p1; \
+ compiletime_assert_atomic_type(*p); \
+ switch (sizeof(*p)) { \
+ case 4: \
+ asm volatile ("ldar %w0, %1" \
+ : "=r" (___p1) : "Q" (*p) : "memory"); \
+ break; \
+ case 8: \
+ asm volatile ("ldar %0, %1" \
+ : "=r" (___p1) : "Q" (*p) : "memory"); \
+ break; \
+ } \
+ ___p1; \
+})
+
#endif
#define read_barrier_depends() do { } while(0)
--- a/arch/ia64/include/asm/barrier.h
+++ b/arch/ia64/include/asm/barrier.h
@@ -45,14 +45,37 @@
# define smp_rmb() rmb()
# define smp_wmb() wmb()
# define smp_read_barrier_depends() read_barrier_depends()
+
#else
+
# define smp_mb() barrier()
# define smp_rmb() barrier()
# define smp_wmb() barrier()
# define smp_read_barrier_depends() do { } while(0)
+
#endif
/*
+ * IA64 GCC turns volatile stores into st.rel and volatile loads into ld.acq no
+ * need for asm trickery!
+ */
+
+#define smp_store_release(p, v) \
+do { \
+ compiletime_assert_atomic_type(*p); \
+ barrier(); \
+ ACCESS_ONCE(*p) = (v); \
+} while (0)
+
+#define smp_load_acquire(p) \
+({ \
+ typeof(*p) ___p1 = ACCESS_ONCE(*p); \
+ compiletime_assert_atomic_type(*p); \
+ barrier(); \
+ ___p1; \
+})
+
+/*
* XXX check on this ---I suspect what Linus really wants here is
* acquire vs release semantics but we can't discuss this stuff with
* Linus just yet. Grrr...
--- a/arch/metag/include/asm/barrier.h
+++ b/arch/metag/include/asm/barrier.h
@@ -82,4 +82,19 @@ static inline void fence(void)
#define smp_read_barrier_depends() do { } while (0)
#define set_mb(var, value) do { var = value; smp_mb(); } while (0)
+#define smp_store_release(p, v) \
+do { \
+ compiletime_assert_atomic_type(*p); \
+ smp_mb(); \
+ ACCESS_ONCE(*p) = (v); \
+} while (0)
+
+#define smp_load_acquire(p) \
+({ \
+ typeof(*p) ___p1 = ACCESS_ONCE(*p); \
+ compiletime_assert_atomic_type(*p); \
+ smp_mb(); \
+ ___p1; \
+})
+
#endif /* _ASM_METAG_BARRIER_H */
--- a/arch/mips/include/asm/barrier.h
+++ b/arch/mips/include/asm/barrier.h
@@ -180,4 +180,19 @@
#define nudge_writes() mb()
#endif
+#define smp_store_release(p, v) \
+do { \
+ compiletime_assert_atomic_type(*p); \
+ smp_mb(); \
+ ACCESS_ONCE(*p) = (v); \
+} while (0)
+
+#define smp_load_acquire(p) \
+({ \
+ typeof(*p) ___p1 = ACCESS_ONCE(*p); \
+ compiletime_assert_atomic_type(*p); \
+ smp_mb(); \
+ ___p1; \
+})
+
#endif /* __ASM_BARRIER_H */
--- a/arch/powerpc/include/asm/barrier.h
+++ b/arch/powerpc/include/asm/barrier.h
@@ -45,11 +45,15 @@
# define SMPWMB eieio
#endif
+#define __lwsync() __asm__ __volatile__ (stringify_in_c(LWSYNC) : : :"memory")
+
#define smp_mb() mb()
-#define smp_rmb() __asm__ __volatile__ (stringify_in_c(LWSYNC) : : :"memory")
+#define smp_rmb() __lwsync()
#define smp_wmb() __asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
#define smp_read_barrier_depends() read_barrier_depends()
#else
+#define __lwsync() barrier()
+
#define smp_mb() barrier()
#define smp_rmb() barrier()
#define smp_wmb() barrier()
@@ -65,4 +69,19 @@
#define data_barrier(x) \
asm volatile("twi 0,%0,0; isync" : : "r" (x) : "memory");
+#define smp_store_release(p, v) \
+do { \
+ compiletime_assert_atomic_type(*p); \
+ __lwsync(); \
+ ACCESS_ONCE(*p) = (v); \
+} while (0)
+
+#define smp_load_acquire(p) \
+({ \
+ typeof(*p) ___p1 = ACCESS_ONCE(*p); \
+ compiletime_assert_atomic_type(*p); \
+ __lwsync(); \
+ ___p1; \
+})
+
#endif /* _ASM_POWERPC_BARRIER_H */
--- a/arch/s390/include/asm/barrier.h
+++ b/arch/s390/include/asm/barrier.h
@@ -32,4 +32,19 @@
#define set_mb(var, value) do { var = value; mb(); } while (0)
+#define smp_store_release(p, v) \
+do { \
+ compiletime_assert_atomic_type(*p); \
+ barrier(); \
+ ACCESS_ONCE(*p) = (v); \
+} while (0)
+
+#define smp_load_acquire(p) \
+({ \
+ typeof(*p) ___p1 = ACCESS_ONCE(*p); \
+ compiletime_assert_atomic_type(*p); \
+ barrier(); \
+ ___p1; \
+})
+
#endif /* __ASM_BARRIER_H */
--- a/arch/sparc/include/asm/barrier_64.h
+++ b/arch/sparc/include/asm/barrier_64.h
@@ -53,4 +53,19 @@ do { __asm__ __volatile__("ba,pt %%xcc,
#define smp_read_barrier_depends() do { } while(0)
+#define smp_store_release(p, v) \
+do { \
+ compiletime_assert_atomic_type(*p); \
+ barrier(); \
+ ACCESS_ONCE(*p) = (v); \
+} while (0)
+
+#define smp_load_acquire(p) \
+({ \
+ typeof(*p) ___p1 = ACCESS_ONCE(*p); \
+ compiletime_assert_atomic_type(*p); \
+ barrier(); \
+ ___p1; \
+})
+
#endif /* !(__SPARC64_BARRIER_H) */
--- a/arch/x86/include/asm/barrier.h
+++ b/arch/x86/include/asm/barrier.h
@@ -92,12 +92,53 @@
#endif
#define smp_read_barrier_depends() read_barrier_depends()
#define set_mb(var, value) do { (void)xchg(&var, value); } while (0)
-#else
+#else /* !SMP */
#define smp_mb() barrier()
#define smp_rmb() barrier()
#define smp_wmb() barrier()
#define smp_read_barrier_depends() do { } while (0)
#define set_mb(var, value) do { var = value; barrier(); } while (0)
+#endif /* SMP */
+
+#if defined(CONFIG_X86_OOSTORE) || defined(CONFIG_X86_PPRO_FENCE)
+
+/*
+ * For either of these options x86 doesn't have a strong TSO memory
+ * model and we should fall back to full barriers.
+ */
+
+#define smp_store_release(p, v) \
+do { \
+ compiletime_assert_atomic_type(*p); \
+ smp_mb(); \
+ ACCESS_ONCE(*p) = (v); \
+} while (0)
+
+#define smp_load_acquire(p) \
+({ \
+ typeof(*p) ___p1 = ACCESS_ONCE(*p); \
+ compiletime_assert_atomic_type(*p); \
+ smp_mb(); \
+ ___p1; \
+})
+
+#else /* regular x86 TSO memory ordering */
+
+#define smp_store_release(p, v) \
+do { \
+ compiletime_assert_atomic_type(*p); \
+ barrier(); \
+ ACCESS_ONCE(*p) = (v); \
+} while (0)
+
+#define smp_load_acquire(p) \
+({ \
+ typeof(*p) ___p1 = ACCESS_ONCE(*p); \
+ compiletime_assert_atomic_type(*p); \
+ barrier(); \
+ ___p1; \
+})
+
#endif
/*
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -62,5 +62,20 @@
#define set_mb(var, value) do { (var) = (value); mb(); } while (0)
#endif
+#define smp_store_release(p, v) \
+do { \
+ compiletime_assert_atomic_type(*p); \
+ smp_mb(); \
+ ACCESS_ONCE(*p) = (v); \
+} while (0)
+
+#define smp_load_acquire(p) \
+({ \
+ typeof(*p) ___p1 = ACCESS_ONCE(*p); \
+ compiletime_assert_atomic_type(*p); \
+ smp_mb(); \
+ ___p1; \
+})
+
#endif /* !__ASSEMBLY__ */
#endif /* __ASM_GENERIC_BARRIER_H */
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -298,6 +298,11 @@ void ftrace_likely_update(struct ftrace_
# define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
#endif
+/* Is this type a native word size -- useful for atomic operations */
+#ifndef __native_word
+# define __native_word(t) (sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long))
+#endif
+
/* Compile time object size, -1 for unknown */
#ifndef __compiletime_object_size
# define __compiletime_object_size(obj) -1
@@ -337,6 +342,10 @@ void ftrace_likely_update(struct ftrace_
#define compiletime_assert(condition, msg) \
_compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
+#define compiletime_assert_atomic_type(t) \
+ compiletime_assert(__native_word(t), \
+ "Need native word sized stores/loads for atomicity.")
+
/*
* Prevent the compiler from merging or refetching accesses. The compiler
* is also forbidden from reordering successive instances of ACCESS_ONCE(),
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH 0/4] arch: Introduce smp_load_acquire() and smp_store_release()
2013-12-18 19:08 [PATCH 0/4] arch: Introduce smp_load_acquire() and smp_store_release() Peter Zijlstra
` (3 preceding siblings ...)
2013-12-18 19:08 ` [PATCH 4/4] arch: Introduce smp_load_acquire(), smp_store_release() Peter Zijlstra
@ 2013-12-18 20:55 ` Paul E. McKenney
4 siblings, 0 replies; 6+ messages in thread
From: Paul E. McKenney @ 2013-12-18 20:55 UTC (permalink / raw)
To: Peter Zijlstra
Cc: linux-arch, linux-kernel, geert, torvalds, VICTORK, oleg, anton,
benh, fweisbec, mathieu.desnoyers, michael, mikey, linux,
schwidefsky, heiko.carstens, tony.luck
On Wed, Dec 18, 2013 at 08:08:06PM +0100, Peter Zijlstra wrote:
>
> This should hopefully be the last posting of this series -- people felt it
> needed one more mostly because last time I typoed the linux-kernel email
> address.
>
> If there are no further comments, Ingo will merge these patches in the next few
> days.
They still look good to me!
Thanx, Paul
> ---
>
> These patches introduce 2 new barrier primitives:
>
> smp_load_acquire(p)
> smp_store_release(p, v)
>
> See the first patch, which changes Documentation/memory-barriers.txt, to find
> the exact definitions of what an ACQUIRE/RELEASE barrier is -- previously known
> as LOCK/UNLOCK barriers.
>
> The second patch moves the smp_mb__{before,after}_atomic_{dec,inc}() barriers
> to asm/atomic.h for arc and hexagon -- they were already there for all other archs.
>
> This cleans up asm/barrier.h, and the third patch makes more agressive use of
> asm-generic/barrier.h to implement the simple cases.
>
> Then the fourth patch adds the new primitives.
>
> Previous versions were widely build tested -- this version is not, but it also
> not significantly different.
>
> These patches apply to:
>
> tip/master
>
>
> ---
> Changes since the last version -- lkml.kernel.org/r/20131213145657.265414969@infradead.org
>
> - fixed linux-kernel email address
> - updated the Documentation patch
>
^ permalink raw reply [flat|nested] 6+ messages in thread