[PATCH] acquire mmap semaphore in pagemap_read.

[Martin Schwidefsky]

From: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>

The walk_page_range function may only be called while holding the mmap
semaphore. Otherwise a concurrent munmap could free a page table that
is read by the generic page table walker.

Cc: Matt Mackall <mpm@xxxxxxxxxxx>
Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
---

 fs/proc/task_mmu.c |    2 ++
 1 file changed, 2 insertions(+)

diff -urpN linux-2.6/fs/proc/task_mmu.c linux-2.6-patched/fs/proc/task_mmu.c
--- linux-2.6/fs/proc/task_mmu.c	2009-03-12 11:32:51.000000000 +0100
+++ linux-2.6-patched/fs/proc/task_mmu.c	2009-03-12 11:33:16.000000000 +0100
@@ -716,7 +716,9 @@ static ssize_t pagemap_read(struct file 
 	 * user buffer is tracked in "pm", and the walk
 	 * will stop when we hit the end of the buffer.
 	 */
+	down_read(&mm->mmap_sem);
 	ret = walk_page_range(start_vaddr, end_vaddr, &pagemap_walk);
+	up_read(&mm->mmap_sem);
 	if (ret == PM_END_OF_BUFFER)
 		ret = 0;
 	/* don't need mmap_sem for these, but this looks cleaner */
--
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