[ARM] Do not call flush_cache_user_range with mmap_sem held
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>
diff --git a/arch/arm/include/asm/cacheflush.h b/arch/arm/include/asm/cacheflush.h
index d5d8d5c..1252a26 100644
--- a/arch/arm/include/asm/cacheflush.h
+++ b/arch/arm/include/asm/cacheflush.h
@@ -249,7 +249,7 @@
* 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 d52eec2..d1a0892 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -451,7 +451,9 @@
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);
}