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Commit b7d25282 authored by Jeff Mahoney's avatar Jeff Mahoney Committed by Greg Kroah-Hartman
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reiserfs: fix race in prealloc discard 



commit 08db141b5313ac2f64b844fb5725b8d81744b417 upstream.

The main loop in __discard_prealloc is protected by the reiserfs write lock
which is dropped across schedules like the BKL it replaced.  The problem is
that it checks the value, calls a routine that schedules, and then adjusts
the state.  As a result, two threads that are calling
reiserfs_prealloc_discard at the same time can race when one calls
reiserfs_free_prealloc_block, the lock is dropped, and the other calls
reiserfs_free_prealloc_block with the same block number.  In the right
circumstances, it can cause the prealloc count to go negative.

Signed-off-by: default avatarJeff Mahoney <jeffm@suse.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 898eeca0

fs/reiserfs/bitmap.c

+10 −2
Original line number Diff line number Diff line
@@ -513,9 +513,17 @@ static void __discard_prealloc(struct reiserfs_transaction_handle *th, 
			       "inode has negative prealloc blocks count.");

#endif

	while (ei->i_prealloc_count > 0) {

		reiserfs_free_prealloc_block(th, inode, ei->i_prealloc_block);

		ei->i_prealloc_block++;

		b_blocknr_t block_to_free;



		/*

		 * reiserfs_free_prealloc_block can drop the write lock,

		 * which could allow another caller to free the same block.

		 * We can protect against it by modifying the prealloc

		 * state before calling it.

		 */

		block_to_free = ei->i_prealloc_block++;

		ei->i_prealloc_count--;

		reiserfs_free_prealloc_block(th, inode, block_to_free);

		dirty = 1;

	}

	if (dirty)