This is a note to let you know that I've just added the patch titled
reiserfs: fix race in prealloc discard
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
reiserfs-fix-race-in-prealloc-discard.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 08db141b5313ac2f64b844fb5725b8d81744b417 Mon Sep 17 00:00:00 2001
From: Jeff Mahoney <jeffm@xxxxxxxx>
Date: Thu, 22 Jun 2017 16:47:34 -0400
Subject: reiserfs: fix race in prealloc discard
From: Jeff Mahoney <jeffm@xxxxxxxx>
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: Jeff Mahoney <jeffm@xxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/reiserfs/bitmap.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
--- a/fs/reiserfs/bitmap.c
+++ b/fs/reiserfs/bitmap.c
@@ -513,9 +513,17 @@ static void __discard_prealloc(struct re
"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)
Patches currently in stable-queue which might be from jeffm@xxxxxxxx are
queue-4.9/reiserfs-don-t-preallocate-blocks-for-extended-attributes.patch
queue-4.9/reiserfs-fix-race-in-prealloc-discard.patch