[lkml]   [2018]   [Jan]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH 3.18 32/52] reiserfs: fix race in prealloc discard
3.18-stable review patch.  If anyone has any objections, please let me know.


From: Jeff Mahoney <>

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 <>
Signed-off-by: Jan Kara <>
Signed-off-by: Greg Kroah-Hartman <>

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.");
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++;
+ reiserfs_free_prealloc_block(th, inode, block_to_free);
dirty = 1;
if (dirty)

 \ /
  Last update: 2018-01-29 21:50    [W:0.456 / U:1.132 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site