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authorJeff Mahoney <jeffm@suse.com>2017-06-22 23:47:34 +0300
committerJan Kara <jack@suse.cz>2017-06-23 10:40:30 +0300
commit08db141b5313ac2f64b844fb5725b8d81744b417 (patch)
tree377bea15d7bbcc73f800c0be9938d69000ad09e8 /fs/reiserfs/bitmap.c
parent54930dfeb46e978b447af0fb8ab4e181c1bf9d7a (diff)
downloadlinux-08db141b5313ac2f64b844fb5725b8d81744b417.tar.xz
reiserfs: fix race in prealloc discard
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@suse.com> Signed-off-by: Jan Kara <jack@suse.cz>
Diffstat (limited to 'fs/reiserfs/bitmap.c')
-rw-r--r--fs/reiserfs/bitmap.c12
1 files changed, 10 insertions, 2 deletions
diff --git a/fs/reiserfs/bitmap.c b/fs/reiserfs/bitmap.c
index a6f39fe2b664..edc8ef78b63f 100644
--- a/fs/reiserfs/bitmap.c
+++ b/fs/reiserfs/bitmap.c
@@ -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)