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mm, sched: Allow uaccess in atomic with pagefault_disable()

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This changes might_fault() so that it does not
trigger a false positive diagnostic for e.g. the following
sequence:

	spin_lock_irqsave()
	pagefault_disable()
	copy_to_user()
	pagefault_enable()
	spin_unlock_irqrestore()

In particular vhost wants to do this, to call
socket ops from under a lock.

There are 3 cases to consider:

 - CONFIG_PROVE_LOCKING - might_fault is non-inline
   so it's easy to move the in_atomic test to fix
   up the false positive warning.

 - CONFIG_DEBUG_ATOMIC_SLEEP - might_fault
   is currently inline, but we are calling a
   non-inline __might_sleep anyway,
   so let's use the non-line version of might_fault
   that does the right thing.

 - !CONFIG_DEBUG_ATOMIC_SLEEP && !CONFIG_PROVE_LOCKING
   __might_sleep is a nop so might_fault is a nop.

Make this explicit.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1369577426-26721-11-git-send-email-mst@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Michael S. Tsirkin 2013-05-26 17:32:23 +03:00 committed by Ingo Molnar
parent 114276ac0a
commit 662bbcb274
2 changed files with 9 additions and 9 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

7
include/linux/kernel.h
View file

@ -193,13 +193,10 @@ extern int _cond_resched(void);
(__x < 0) ? -__x : __x; \
})
#ifdef CONFIG_PROVE_LOCKING
#if defined(CONFIG_PROVE_LOCKING) || defined(CONFIG_DEBUG_ATOMIC_SLEEP)
void might_fault(void);
#else
static inline void might_fault(void)
{
__might_sleep(__FILE__, __LINE__, 0);
}
static inline void might_fault(void) { }
#endif
extern struct atomic_notifier_head panic_notifier_list;

11
mm/memory.c
View file

@ -4210,7 +4210,7 @@ void print_vma_addr(char *prefix, unsigned long ip)
up_read(&mm->mmap_sem);
}
#ifdef CONFIG_PROVE_LOCKING
#if defined(CONFIG_PROVE_LOCKING) || defined(CONFIG_DEBUG_ATOMIC_SLEEP)
void might_fault(void)
{
/*
@ -4222,14 +4222,17 @@ void might_fault(void)
if (segment_eq(get_fs(), KERNEL_DS))
return;
__might_sleep(__FILE__, __LINE__, 0);
/*
* it would be nicer only to annotate paths which are not under
* pagefault_disable, however that requires a larger audit and
* providing helpers like get_user_atomic.
*/
if (!in_atomic() && current->mm)
if (in_atomic())
return;
__might_sleep(__FILE__, __LINE__, 0);
if (current->mm)
might_lock_read(&current->mm->mmap_sem);
}
EXPORT_SYMBOL(might_fault);