Commit 662bbcb2 authored May 26, 2013 by Michael S. Tsirkin Committed by Ingo Molnar May 28, 2013

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: 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>

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);

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