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Commit 662bbcb2 authored by Michael S. Tsirkin's avatar Michael S. Tsirkin Committed by Ingo Molnar
Browse files

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



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: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarPeter 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: default avatarIngo Molnar <mingo@kernel.org>
parent 114276ac

include/linux/kernel.h

+2 −5
Original line number Diff line number Diff line
@@ -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;

mm/memory.c

+7 −4
Original line number Diff line number Diff line
@@ -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);