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| author | Jan Kara <jack@suse.cz> | 2014-02-20 17:02:27 +0100 |
|---|---|---|
| committer | Jan Kara <jack@suse.cz> | 2014-02-20 21:57:04 +0100 |
| commit | 1362f4ea20fa63688ba6026e586d9746ff13a846 (patch) | |
| tree | 6c80329bee77974426663a1af8e5d70ef62759f9 | |
| parent | 09ebb17ab476b6ac1cc07b53d07e88f4d31ee4d3 (diff) | |
| download | kernel-common-1362f4ea20fa63688ba6026e586d9746ff13a846.tar.gz kernel-common-1362f4ea20fa63688ba6026e586d9746ff13a846.tar.bz2 kernel-common-1362f4ea20fa63688ba6026e586d9746ff13a846.zip | |
quota: Fix race between dqput() and dquot_scan_active()
Currently last dqput() can race with dquot_scan_active() causing it to
call callback for an already deactivated dquot. The race is as follows:
CPU1 CPU2
dqput()
spin_lock(&dq_list_lock);
if (atomic_read(&dquot->dq_count) > 1) {
- not taken
if (test_bit(DQ_ACTIVE_B, &dquot->dq_flags)) {
spin_unlock(&dq_list_lock);
->release_dquot(dquot);
if (atomic_read(&dquot->dq_count) > 1)
- not taken
dquot_scan_active()
spin_lock(&dq_list_lock);
if (!test_bit(DQ_ACTIVE_B, &dquot->dq_flags))
- not taken
atomic_inc(&dquot->dq_count);
spin_unlock(&dq_list_lock);
- proceeds to release dquot
ret = fn(dquot, priv);
- called for inactive dquot
Fix the problem by making sure possible ->release_dquot() is finished by
the time we call the callback and new calls to it will notice reference
dquot_scan_active() has taken and bail out.
CC: stable@vger.kernel.org # >= 2.6.29
Signed-off-by: Jan Kara <jack@suse.cz>
| -rw-r--r-- | fs/quota/dquot.c | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c index 831d49a4111f..cfc8dcc16043 100644 --- a/fs/quota/dquot.c +++ b/fs/quota/dquot.c @@ -581,9 +581,17 @@ int dquot_scan_active(struct super_block *sb, dqstats_inc(DQST_LOOKUPS); dqput(old_dquot); old_dquot = dquot; - ret = fn(dquot, priv); - if (ret < 0) - goto out; + /* + * ->release_dquot() can be racing with us. Our reference + * protects us from new calls to it so just wait for any + * outstanding call and recheck the DQ_ACTIVE_B after that. + */ + wait_on_dquot(dquot); + if (test_bit(DQ_ACTIVE_B, &dquot->dq_flags)) { + ret = fn(dquot, priv); + if (ret < 0) + goto out; + } spin_lock(&dq_list_lock); /* We are safe to continue now because our dquot could not * be moved out of the inuse list while we hold the reference */ |