* Re: [PULL] Trivial macros to help cpumask conversion in linux-next: tsk_cpumask and mm_cpumask
2009-03-03 22:12 ` Linus Torvalds
@ 2009-03-04 1:16 ` Rusty Russell
0 siblings, 0 replies; 3+ messages in thread
From: Rusty Russell @ 2009-03-04 1:16 UTC (permalink / raw)
To: Linus Torvalds; +Cc: Ingo Molnar, Mike Travis, linux-kernel
On Wednesday 04 March 2009 08:42:09 Linus Torvalds wrote:
>
> On Tue, 3 Mar 2009, Rusty Russell wrote:
> >
> > Rusty Russell (2):
> > cpumask: tsk_cpumask for accessing the struct task_struct's cpus_allowed.
> > cpumask: mm_cpumask for accessing the struct mm_struct's cpu_vm_mask.
>
> I really want to know the _reason_ for things like this, not just a
> trivial patch that adds a stupid macro "for the future".
Sorry, should have been more explicit.
cpumask_t -> cpumask_var_t breaks all the users (since it looks like a
pointer). So I decided wrappers were in order while I feed the conversion
patches via all the arch maintainers & linux-next.
(In fact, we probably want to use a dangling bitmap in these cases,
rather than a double alloc for CONFIG_CPUMASK_OFFSTACK=y, tho various
places use sizeof(struct task_struct) making this a little nasty).
Not that we *really* care about the size of these structs; but it does
allow us to make 'struct cpumask' undefined for CONFIG_CPUMASK_OFFSTACK=y
so noone can accidentally create one on the stack, or use *mask1 = *mask2.
FYI, here's the final conversion patch:
cpumask: convert task_struct cpus_allowed to dangling bitmap.
Rather than use the standard [] or [0] array, I truncate the struct
when CONFIG_CPUMASK_OFFSTACK=y. This avoids complications with
INIT_TASK and sizeof(struct task_struct).
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---
include/linux/init_task.h | 2 +-
include/linux/sched.h | 7 +++++--
kernel/fork.c | 18 +++++++++++++++++-
3 files changed, 23 insertions(+), 4 deletions(-)
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -136,7 +136,7 @@ extern struct cred init_cred;
.static_prio = MAX_PRIO-20, \
.normal_prio = MAX_PRIO-20, \
.policy = SCHED_NORMAL, \
- .cpus_allowed = CPU_MASK_ALL, \
+ .cpus_allowed = CPU_BITS_ALL, \
.mm = NULL, \
.active_mm = &init_mm, \
.se = { \
diff --git a/include/linux/sched.h b/include/linux/sched.h
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1135,7 +1135,6 @@ struct task_struct {
#endif
unsigned int policy;
- cpumask_t cpus_allowed;
#ifdef CONFIG_PREEMPT_RCU
int rcu_read_lock_nesting;
@@ -1400,10 +1399,14 @@ struct task_struct {
/* state flags for use by tracers */
unsigned long trace;
#endif
+
+ /* This has to go at the end: if CONFIG_CPUMASK_OFFSTACK=y, only
+ * nr_cpu_ids bits will actually be allocated. */
+ DECLARE_BITMAP(cpus_allowed, CONFIG_NR_CPUS);
};
/* Future-safe accessor for struct task_struct's cpus_allowed. */
-#define tsk_cpumask(tsk) (&(tsk)->cpus_allowed)
+#define tsk_cpumask(tsk) (to_cpumask((tsk)->cpus_allowed))
/*
* Priority of a process goes from 0..MAX_PRIO-1, valid RT
diff --git a/kernel/fork.c b/kernel/fork.c
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -173,9 +173,25 @@ void __init fork_init(unsigned long memp
#ifndef ARCH_MIN_TASKALIGN
#define ARCH_MIN_TASKALIGN L1_CACHE_BYTES
#endif
+ unsigned int task_size;
+
+#ifdef CONFIG_CPUMASK_OFFSTACK
+ /*
+ * Restrict task_struct allocations so cpus_allowed is only
+ * nr_cpu_ids long. cpus_allowed must be a NR_CPUS bitmap at
+ * end for this to work.
+ */
+ BUILD_BUG_ON(offsetof(struct task_struct, cpus_allowed)
+ + BITS_TO_LONGS(CONFIG_NR_CPUS)*sizeof(long)
+ != sizeof(struct task_struct));
+ task_size = offsetof(struct task_struct, cpus_allowed) +
+ BITS_TO_LONGS(nr_cpu_ids) * sizeof(long);
+#else
+ task_size = sizeof(struct task_struct);
+#endif
/* create a slab on which task_structs can be allocated */
task_struct_cachep =
- kmem_cache_create("task_struct", sizeof(struct task_struct),
+ kmem_cache_create("task_struct", task_size,
ARCH_MIN_TASKALIGN, SLAB_PANIC, NULL);
#endif
^ permalink raw reply [flat|nested] 3+ messages in thread