[PATCH] [ARM] Do not call flush_cache_user_range with mmap_sem held
Dima Zavin
dima at android.com
Wed Apr 28 03:32:11 EDT 2010
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.
Signed-off-by: Dima Zavin <dima at android.com>
Cc: Russell King <rmk+kernel at arm.linux.org.uk>
Cc: Arve Hjønnevåg <arve at android.com>
---
arch/arm/include/asm/cacheflush.h | 2 +-
arch/arm/kernel/traps.c | 4 +++-
2 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/arch/arm/include/asm/cacheflush.h b/arch/arm/include/asm/cacheflush.h
index 0d08d41..b68a2b4 100644
--- a/arch/arm/include/asm/cacheflush.h
+++ b/arch/arm/include/asm/cacheflush.h
@@ -336,7 +336,7 @@ extern void flush_cache_page(struct vm_area_struct *vma, unsigned long user_addr
* 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))
/*
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 1621e53..2455fd3 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -453,7 +453,9 @@ 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);
}
--
1.6.6
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