[RFC 2/2] mm, sched: trigger might_sleep() in might_fault() when atomic

From: David Hildenbrand
Date: Tue Nov 25 2014 - 06:44:20 EST


Commit 662bbcb2747c2422cf98d3d97619509379eee466 disabled in atomic checks
for all user access code (that uses might_fault()).

That change basically disabled CONFIG_DEBUG_ATOMIC_SLEEP for all user access
functions. However, this is a mighty debugging aid that we want.

If user memory is to be accessed while pagefault_disabled() is set, the atomic
variants of copy_(to|from)_user can be used.

This patch reverts commit 662bbcb2747c2422cf98d3d97619509379eee466 taking care
of the !MMU optimization.

Signed-off-by: David Hildenbrand <dahi@xxxxxxxxxxxxxxxxxx>
---
include/linux/kernel.h | 8 ++++++--
mm/memory.c | 11 ++++-------
2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 3d770f55..1d3397c 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -225,9 +225,13 @@ static inline u32 reciprocal_scale(u32 val, u32 ep_ro)
return (u32)(((u64) val * ep_ro) >> 32);
}

-#if defined(CONFIG_MMU) && \
- (defined(CONFIG_PROVE_LOCKING) || defined(CONFIG_DEBUG_ATOMIC_SLEEP))
+#if defined(CONFIG_MMU) && defined(CONFIG_PROVE_LOCKING)
void might_fault(void);
+#elif defined(CONFIG_MMU) && defined(CONFIG_DEBUG_ATOMIC_SLEEP)
+static inline void might_fault(void)
+{
+ __might_sleep(__FILE__, __LINE__, 0);
+}
#else
static inline void might_fault(void) { }
#endif
diff --git a/mm/memory.c b/mm/memory.c
index 3e50383..fe0c815 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3699,7 +3699,7 @@ void print_vma_addr(char *prefix, unsigned long ip)
up_read(&mm->mmap_sem);
}

-#if defined(CONFIG_PROVE_LOCKING) || defined(CONFIG_DEBUG_ATOMIC_SLEEP)
+#ifdef CONFIG_PROVE_LOCKING
void might_fault(void)
{
/*
@@ -3711,17 +3711,14 @@ 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())
- return;
-
- __might_sleep(__FILE__, __LINE__, 0);
-
- if (current->mm)
+ if (!in_atomic() && current->mm)
might_lock_read(&current->mm->mmap_sem);
}
EXPORT_SYMBOL(might_fault);
--
1.8.5.5

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