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author | Jeff Mahoney <jeffm@suse.com> | 2013-09-23 16:50:42 -0400 |
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committer | Jan Kara <jack@suse.cz> | 2013-09-24 11:24:21 +0200 |
commit | 721a769c034204e8e5f6ca4ecbff249e0225333b (patch) | |
tree | f73faca4b745d8250d09708781455d59bf65168d /fs/reiserfs/journal.c | |
parent | 7bc9cc07ee5bbac58bab88e8a5d6e32785f8fd32 (diff) | |
download | linux-721a769c034204e8e5f6ca4ecbff249e0225333b.tar.gz linux-721a769c034204e8e5f6ca4ecbff249e0225333b.tar.bz2 linux-721a769c034204e8e5f6ca4ecbff249e0225333b.zip |
reiserfs: fix race with flush_used_journal_lists and flush_journal_list
There are two locks involved in managing the journal lists. The general
reiserfs_write_lock and the journal->j_flush_mutex.
While flush_journal_list is sleeping to acquire the j_flush_mutex or to
submit a block for write, it will drop the write lock. This allows
another thread to acquire the write lock and ultimately call
flush_used_journal_lists to traverse the list of journal lists and
select one for flushing. It can select the journal_list that has just
had flush_journal_list called on it in the original thread and call it
again with the same journal_list.
The second thread then drops the write lock to acquire j_flush_mutex and
the first thread reacquires it and continues execution and eventually
clears and frees the journal list before dropping j_flush_mutex and
returning.
The second thread acquires j_flush_mutex and ends up operating on a
journal_list that has already been released. If the memory hasn't
been reused, we'll soon after hit a BUG_ON because the transaction id
has already been cleared. If it's been reused, we'll crash in other
fun ways.
Since flush_journal_list will synchronize on j_flush_mutex, we can fix
the race by taking a proper reference in flush_used_journal_lists
and checking to see if it's still valid after the mutex is taken. It's
safe to iterate the list of journal lists and pick a list with
just the write lock as long as a reference is taken on the journal list
before we drop the lock. We already have code to handle whether a
transaction has been flushed already so we can use that to handle the
race and get rid of the trans_id BUG_ON.
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Diffstat (limited to 'fs/reiserfs/journal.c')
-rw-r--r-- | fs/reiserfs/journal.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/fs/reiserfs/journal.c b/fs/reiserfs/journal.c index 7a37473b44dd..fd777032c2ba 100644 --- a/fs/reiserfs/journal.c +++ b/fs/reiserfs/journal.c @@ -1338,7 +1338,6 @@ static int flush_journal_list(struct super_block *s, reiserfs_warning(s, "clm-2048", "called with wcount %d", atomic_read(&journal->j_wcount)); } - BUG_ON(jl->j_trans_id == 0); /* if flushall == 0, the lock is already held */ if (flushall) { @@ -1765,6 +1764,8 @@ static int flush_used_journal_lists(struct super_block *s, break; tjl = JOURNAL_LIST_ENTRY(tjl->j_list.next); } + get_journal_list(jl); + get_journal_list(flush_jl); /* try to find a group of blocks we can flush across all the ** transactions, but only bother if we've actually spanned ** across multiple lists @@ -1773,6 +1774,8 @@ static int flush_used_journal_lists(struct super_block *s, ret = kupdate_transactions(s, jl, &tjl, &trans_id, len, i); } flush_journal_list(s, flush_jl, 1); + put_journal_list(s, flush_jl); + put_journal_list(s, jl); return 0; } |