[PATCH v2 02/26] mm: userfault: return VM_FAULT_RETRY on signals

Peter Xu
2019-02-12T02:57:10Z

The idea comes from the upstream discussion between Linus and Andrea:

https://lkml.org/lkml/2017/10/30/560

A summary to the issue: there was a special path in handle_userfault()
in the past that we'll return a VM_FAULT_NOPAGE when we detected
non-fatal signals when waiting for userfault handling. We did that by
reacquiring the mmap_sem before returning. However that brings a risk
in that the vmas might have changed when we retake the mmap_sem and
even we could be holding an invalid vma structure.

This patch removes the special path and we'll return a VM_FAULT_RETRY
with the common path even if we have got such signals. Then for all
the architectures that is passing in VM_FAULT_ALLOW_RETRY into
handle_mm_fault(), we check not only for SIGKILL but for all the rest
of userspace pending signals right after we returned from
handle_mm_fault(). This can allow the userspace to handle nonfatal
signals faster than before.

This patch is a preparation work for the next patch to finally remove
the special code path mentioned above in handle_userfault().

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
arch/alpha/mm/fault.c | 2 +-
arch/arc/mm/fault.c | 11 ++++-------
arch/arm/mm/fault.c | 6 +++---
arch/arm64/mm/fault.c | 6 +++---
arch/hexagon/mm/vm_fault.c | 2 +-
arch/ia64/mm/fault.c | 2 +-
arch/m68k/mm/fault.c | 2 +-
arch/microblaze/mm/fault.c | 2 +-
arch/mips/mm/fault.c | 2 +-
arch/nds32/mm/fault.c | 6 +++---
arch/nios2/mm/fault.c | 2 +-
arch/openrisc/mm/fault.c | 2 +-
arch/parisc/mm/fault.c | 2 +-
arch/powerpc/mm/fault.c | 2 ++
arch/riscv/mm/fault.c | 4 ++--
arch/s390/mm/fault.c | 9 ++++++---
arch/sh/mm/fault.c | 4 ++++
arch/sparc/mm/fault_32.c | 3 +++
arch/sparc/mm/fault_64.c | 3 +++
arch/um/kernel/trap.c | 5 ++++-
arch/unicore32/mm/fault.c | 4 ++--
arch/x86/mm/fault.c | 6 +++++-
arch/xtensa/mm/fault.c | 3 +++
23 files changed, 56 insertions(+), 34 deletions(-)

diff --git a/arch/alpha/mm/fault.c b/arch/alpha/mm/fault.c
index d73dc473fbb9..46e5e420ad2a 100644
--- a/arch/alpha/mm/fault.c
+++ b/arch/alpha/mm/fault.c
@@ -150,7 +150,7 @@ do_page_fault(unsigned long address, unsigned long mmcsr,
the fault. */
fault = handle_mm_fault(vma, address, flags);

- if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+ if ((fault & VM_FAULT_RETRY) && signal_pending(current))
return;

if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
index 8df1638259f3..dc5f1b8859d2 100644
--- a/arch/arc/mm/fault.c
+++ b/arch/arc/mm/fault.c
@@ -141,17 +141,14 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
*/
fault = handle_mm_fault(vma, address, flags);

- if (fatal_signal_pending(current)) {
-
+ if (unlikely(fault & VM_FAULT_RETRY && signal_pending(current))) {
+ if (fatal_signal_pending(current) && !user_mode(regs))
+ goto no_context;
/*
* if fault retry, mmap_sem already relinquished by core mm
* so OK to return to user mode (with signal handled first)
*/
- if (fault & VM_FAULT_RETRY) {
- if (!user_mode(regs))
- goto no_context;
- return;
- }
+ return;
}

perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 58f69fa07df9..c41c021bbe40 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -314,12 +314,12 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)

fault = __do_page_fault(mm, addr, fsr, flags, tsk);

- /* If we need to retry but a fatal signal is pending, handle the
+ /* If we need to retry but a signal is pending, handle the
* signal first. We do not need to release the mmap_sem because
* it would already be released in __lock_page_or_retry in
* mm/filemap.c. */
- if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
- if (!user_mode(regs))
+ if (unlikely(fault & VM_FAULT_RETRY && signal_pending(current))) {
+ if (fatal_signal_pending(current) && !user_mode(regs))
goto no_context;
return 0;
}
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index efb7b2cbead5..a38ff8c49a66 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -512,13 +512,13 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,

if (fault & VM_FAULT_RETRY) {
/*
- * If we need to retry but a fatal signal is pending,
+ * If we need to retry but a signal is pending,
* handle the signal first. We do not need to release
* the mmap_sem because it would already be released
* in __lock_page_or_retry in mm/filemap.c.
*/
- if (fatal_signal_pending(current)) {
- if (!user_mode(regs))
+ if (signal_pending(current)) {
+ if (fatal_signal_pending(current) && !user_mode(regs))
goto no_context;
return 0;
}
diff --git a/arch/hexagon/mm/vm_fault.c b/arch/hexagon/mm/vm_fault.c
index eb263e61daf4..be10b441d9cc 100644
--- a/arch/hexagon/mm/vm_fault.c
+++ b/arch/hexagon/mm/vm_fault.c
@@ -104,7 +104,7 @@ void do_page_fault(unsigned long address, long cause, struct pt_regs *regs)

fault = handle_mm_fault(vma, address, flags);

- if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+ if ((fault & VM_FAULT_RETRY) && signal_pending(current))
return;

/* The most common case -- we are done. */
diff --git a/arch/ia64/mm/fault.c b/arch/ia64/mm/fault.c
index 5baeb022f474..62c2d39d2bed 100644
--- a/arch/ia64/mm/fault.c
+++ b/arch/ia64/mm/fault.c
@@ -163,7 +163,7 @@ ia64_do_page_fault (unsigned long address, unsigned long isr, struct pt_regs *re
*/
fault = handle_mm_fault(vma, address, flags);

- if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+ if ((fault & VM_FAULT_RETRY) && signal_pending(current))
return;

if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/m68k/mm/fault.c b/arch/m68k/mm/fault.c
index 9b6163c05a75..d9808a807ab8 100644
--- a/arch/m68k/mm/fault.c
+++ b/arch/m68k/mm/fault.c
@@ -138,7 +138,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
fault = handle_mm_fault(vma, address, flags);
pr_debug("handle_mm_fault returns %x\n", fault);

- if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+ if ((fault & VM_FAULT_RETRY) && signal_pending(current))
return 0;

if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/microblaze/mm/fault.c b/arch/microblaze/mm/fault.c
index 202ad6a494f5..4fd2dbd0c5ca 100644
--- a/arch/microblaze/mm/fault.c
+++ b/arch/microblaze/mm/fault.c
@@ -217,7 +217,7 @@ void do_page_fault(struct pt_regs *regs, unsigned long address,
*/
fault = handle_mm_fault(vma, address, flags);

- if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+ if ((fault & VM_FAULT_RETRY) && signal_pending(current))
return;

if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/mips/mm/fault.c b/arch/mips/mm/fault.c
index 73d8a0f0b810..92374fd091d2 100644
--- a/arch/mips/mm/fault.c
+++ b/arch/mips/mm/fault.c
@@ -154,7 +154,7 @@ static void __kprobes __do_page_fault(struct pt_regs *regs, unsigned long write,
*/
fault = handle_mm_fault(vma, address, flags);

- if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+ if ((fault & VM_FAULT_RETRY) && signal_pending(current))
return;

perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
diff --git a/arch/nds32/mm/fault.c b/arch/nds32/mm/fault.c
index 68d5f2a27f38..9f6e477b9e30 100644
--- a/arch/nds32/mm/fault.c
+++ b/arch/nds32/mm/fault.c
@@ -206,12 +206,12 @@ void do_page_fault(unsigned long entry, unsigned long addr,
fault = handle_mm_fault(vma, addr, flags);

/*
- * If we need to retry but a fatal signal is pending, handle the
+ * If we need to retry but a signal is pending, handle the
* signal first. We do not need to release the mmap_sem because it
* would already be released in __lock_page_or_retry in mm/filemap.c.
*/
- if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
- if (!user_mode(regs))
+ if (fault & VM_FAULT_RETRY && signal_pending(current)) {
+ if (fatal_signal_pending(current) && !user_mode(regs))
goto no_context;
return;
}
diff --git a/arch/nios2/mm/fault.c b/arch/nios2/mm/fault.c
index 24fd84cf6006..5939434a31ae 100644
--- a/arch/nios2/mm/fault.c
+++ b/arch/nios2/mm/fault.c
@@ -134,7 +134,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long cause,
*/
fault = handle_mm_fault(vma, address, flags);

- if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+ if ((fault & VM_FAULT_RETRY) && signal_pending(current))
return;

if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/openrisc/mm/fault.c b/arch/openrisc/mm/fault.c
index dc4dbafc1d83..873ecb5d82d7 100644
--- a/arch/openrisc/mm/fault.c
+++ b/arch/openrisc/mm/fault.c
@@ -165,7 +165,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long address,

fault = handle_mm_fault(vma, address, flags);

- if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+ if ((fault & VM_FAULT_RETRY) && signal_pending(current))
return;

if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/parisc/mm/fault.c b/arch/parisc/mm/fault.c
index c8e8b7c05558..29422eec329d 100644
--- a/arch/parisc/mm/fault.c
+++ b/arch/parisc/mm/fault.c
@@ -303,7 +303,7 @@ void do_page_fault(struct pt_regs *regs, unsigned long code,

fault = handle_mm_fault(vma, address, flags);

- if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+ if ((fault & VM_FAULT_RETRY) && signal_pending(current))
return;

if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 887f11bcf330..aaa853e6592f 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -591,6 +591,8 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
*/
flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
+ if (is_user && signal_pending(current))
+ return 0;
if (!fatal_signal_pending(current))
goto retry;
}
diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
index 88401d5125bc..4fc8d746bec3 100644
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -123,11 +123,11 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
fault = handle_mm_fault(vma, addr, flags);

/*
- * If we need to retry but a fatal signal is pending, handle the
+ * If we need to retry but a signal is pending, handle the
* signal first. We do not need to release the mmap_sem because it
* would already be released in __lock_page_or_retry in mm/filemap.c.
*/
- if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(tsk))
+ if ((fault & VM_FAULT_RETRY) && signal_pending(tsk))
return;

if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 11613362c4e7..aba1dad1efcd 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -476,9 +476,12 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
* the fault.
*/
fault = handle_mm_fault(vma, address, flags);
- /* No reason to continue if interrupted by SIGKILL. */
- if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
- fault = VM_FAULT_SIGNAL;
+ /* Do not continue if interrupted by signals. */
+ if ((fault & VM_FAULT_RETRY) && signal_pending(current)) {
+ if (fatal_signal_pending(current))
+ fault = VM_FAULT_SIGNAL;
+ else
+ fault = 0;
if (flags & FAULT_FLAG_RETRY_NOWAIT)
goto out_up;
goto out;
diff --git a/arch/sh/mm/fault.c b/arch/sh/mm/fault.c
index 6defd2c6d9b1..baf5d73df40c 100644
--- a/arch/sh/mm/fault.c
+++ b/arch/sh/mm/fault.c
@@ -506,6 +506,10 @@ asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
* have already released it in __lock_page_or_retry
* in mm/filemap.c.
*/
+
+ if (user_mode(regs) && signal_pending(tsk))
+ return;
+
goto retry;
}
}
diff --git a/arch/sparc/mm/fault_32.c b/arch/sparc/mm/fault_32.c
index b0440b0edd97..a2c83104fe35 100644
--- a/arch/sparc/mm/fault_32.c
+++ b/arch/sparc/mm/fault_32.c
@@ -269,6 +269,9 @@ asmlinkage void do_sparc_fault(struct pt_regs *regs, int text_fault, int write,
* in mm/filemap.c.
*/

+ if (user_mode(regs) && signal_pending(tsk))
+ return;
+
goto retry;
}
}
diff --git a/arch/sparc/mm/fault_64.c b/arch/sparc/mm/fault_64.c
index 8f8a604c1300..cad71ec5c7b3 100644
--- a/arch/sparc/mm/fault_64.c
+++ b/arch/sparc/mm/fault_64.c
@@ -467,6 +467,9 @@ asmlinkage void __kprobes do_sparc64_fault(struct pt_regs *regs)
* in mm/filemap.c.
*/

+ if (user_mode(regs) && signal_pending(current))
+ return;
+
goto retry;
}
}
diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index 0e8b6158f224..09baf37b65b9 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -76,8 +76,11 @@ int handle_page_fault(unsigned long address, unsigned long ip,

fault = handle_mm_fault(vma, address, flags);

- if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+ if (fault & VM_FAULT_RETRY && signal_pending(current)) {
+ if (is_user && !fatal_signal_pending(current))
+ err = 0;
goto out_nosemaphore;
+ }

if (unlikely(fault & VM_FAULT_ERROR)) {
if (fault & VM_FAULT_OOM) {
diff --git a/arch/unicore32/mm/fault.c b/arch/unicore32/mm/fault.c
index b9a3a50644c1..3611f19234a1 100644
--- a/arch/unicore32/mm/fault.c
+++ b/arch/unicore32/mm/fault.c
@@ -248,11 +248,11 @@ static int do_pf(unsigned long addr, unsigned int fsr, struct pt_regs *regs)

fault = __do_pf(mm, addr, fsr, flags, tsk);

- /* If we need to retry but a fatal signal is pending, handle the
+ /* If we need to retry but a signal is pending, handle the
* signal first. We do not need to release the mmap_sem because
* it would already be released in __lock_page_or_retry in
* mm/filemap.c. */
- if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+ if ((fault & VM_FAULT_RETRY) && signal_pending(current))
return 0;

if (!(fault & VM_FAULT_ERROR) && (flags & FAULT_FLAG_ALLOW_RETRY)) {
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 9d5c75f02295..248ff0a28ecd 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1481,16 +1481,20 @@ void do_user_addr_fault(struct pt_regs *regs,
* that we made any progress. Handle this case first.
*/
if (unlikely(fault & VM_FAULT_RETRY)) {
+ bool is_user = flags & FAULT_FLAG_USER;
+
/* Retry at most once */
if (flags & FAULT_FLAG_ALLOW_RETRY) {
flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
+ if (is_user && signal_pending(tsk))
+ return;
if (!fatal_signal_pending(tsk))
goto retry;
}

/* User mode? Just return to handle the fatal exception */
- if (flags & FAULT_FLAG_USER)
+ if (is_user)
return;

/* Not returning to user mode? Handle exceptions or die: */
diff --git a/arch/xtensa/mm/fault.c b/arch/xtensa/mm/fault.c
index 2ab0e0dcd166..792dad5e2f12 100644
--- a/arch/xtensa/mm/fault.c
+++ b/arch/xtensa/mm/fault.c
@@ -136,6 +136,9 @@ void do_page_fault(struct pt_regs *regs)
* in mm/filemap.c.
*/

+ if (user_mode(regs) && signal_pending(current))
+ return;
+
goto retry;
}
}
--
2.17.1