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x86: some lock annotations for user copy paths

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copy_to/from_user and all its variants (except the atomic ones) can take a
page fault and perform non-trivial work like taking mmap_sem and entering
the filesyste/pagecache.

Unfortunately, this often escapes lockdep because a common pattern is to
use it to read in some arguments just set up from userspace, or write data
back to a hot buffer. In those cases, it will be unlikely for page reclaim
to get a window in to cause copy_*_user to fault.

With the new might_lock primitives, add some annotations to x86. I don't
know if I caught all possible faulting points (it's a bit of a maze, and I
didn't really look at 32-bit). But this is a starting point.

Boots and runs OK so far.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Nick Piggin
2008-09-10 13:37:17 +02:00
committed by Ingo Molnar
parent 76b189e918
commit c10d38dda1
5 changed files with 44 additions and 3 deletions
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7
arch/x86/lib/usercopy_32.c
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@@ -33,6 +33,8 @@ static inline int __movsl_is_ok(unsigned long a1, unsigned long a2, unsigned lon
do { \
int __d0, __d1, __d2; \
might_sleep(); \
if (current->mm) \
might_lock_read(&current->mm->mmap_sem); \
__asm__ __volatile__( \
" testl %1,%1\n" \
" jz 2f\n" \
@@ -120,6 +122,8 @@ EXPORT_SYMBOL(strncpy_from_user);
do { \
int __d0; \
might_sleep(); \
if (current->mm) \
might_lock_read(&current->mm->mmap_sem); \
__asm__ __volatile__( \
"0: rep; stosl\n" \
" movl %2,%0\n" \
@@ -148,7 +152,6 @@ do { \
unsigned long
clear_user(void __user *to, unsigned long n)
{
might_sleep();
if (access_ok(VERIFY_WRITE, to, n))
__do_clear_user(to, n);
return n;
@@ -191,6 +194,8 @@ long strnlen_user(const char __user *s, long n)
unsigned long res, tmp;
might_sleep();
if (current->mm)
might_lock_read(&current->mm->mmap_sem);
__asm__ __volatile__(
" testl %0, %0\n"