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[ARM] Do not call flush_cache_user_range with mmap_sem held

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We can't be holding the mmap_sem while calling flush_cache_user_range
because the flush can fault. If we fault on a user address, the
page fault handler will try to take mmap_sem again. Since both places
acquire the read lock, most of the time it succeeds. However, if another
thread tries to acquire the write lock on the mmap_sem (e.g. mmap) in
between the call to flush_cache_user_range and the fault, the down_read
in do_page_fault will deadlock.

Also, since we really can't be holding the mmap_sem while calling
flush_cache_user_range AND vma is actually unused by the flush itself,
get rid of vma as an argument.

Change-Id: If55409bde41ad1060fa4fe7cbd4ac530d4d9a106
Signed-off-by: Dima Zavin <dima@android.com>
This commit is contained in:
Dima Zavin 2010-04-27 20:57:04 -07:00
commit 7bc14acfbb
2 changed files with 4 additions and 2 deletions
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2
arch/arm/include/asm/cacheflush.h
View file

@ -381,7 +381,7 @@ extern void flush_ptrace_access(struct vm_area_struct *vma, struct page *page,
* Harvard caches are synchronised for the user space address range.
* This is used for the ARM private sys_cacheflush system call.
*/
#define flush_cache_user_range(vma,start,end) \
#define flush_cache_user_range(start,end) \
__cpuc_coherent_user_range((start) & PAGE_MASK, PAGE_ALIGN(end))
/*

4
arch/arm/kernel/traps.c
View file

@ -438,7 +438,9 @@ do_cache_op(unsigned long start, unsigned long end, int flags)
if (end > vma->vm_end)
end = vma->vm_end;
flush_cache_user_range(vma, start, end);
up_read(&mm->mmap_sem);
flush_cache_user_range(start, end);
return;
}
up_read(&mm->mmap_sem);
}