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| author | Jeff Mahoney <jeffm@suse.com> | 2017-06-22 16:47:34 -0400 |
|---|---|---|
| committer | Jan Kara <jack@suse.cz> | 2017-06-23 09:40:30 +0200 |
| commit | 08db141b5313ac2f64b844fb5725b8d81744b417 (patch) | |
| tree | 377bea15d7bbcc73f800c0be9938d69000ad09e8 /fs | |
| parent | 54930dfeb46e978b447af0fb8ab4e181c1bf9d7a (diff) | |
| download | lwn-08db141b5313ac2f64b844fb5725b8d81744b417.tar.gz lwn-08db141b5313ac2f64b844fb5725b8d81744b417.zip | |
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')
| -rw-r--r-- | fs/reiserfs/bitmap.c | 12 |
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) |