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| author | Jan Kara <jack@suse.cz> | 2014-02-20 17:02:27 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-03-06 21:30:12 -0800 |
| commit | 4480120a6cf3c834cc73431d615bb716be586f2f (patch) | |
| tree | 2295f596dcce1c61a092008eba09a9d034019122 | |
| parent | 3e66969eabfa905623cd6677c08e523a6b9410da (diff) | |
| download | linux-stable-4480120a6cf3c834cc73431d615bb716be586f2f.tar.gz linux-stable-4480120a6cf3c834cc73431d615bb716be586f2f.tar.bz2 linux-stable-4480120a6cf3c834cc73431d615bb716be586f2f.zip | |
quota: Fix race between dqput() and dquot_scan_active()
commit 1362f4ea20fa63688ba6026e586d9746ff13a846 upstream.
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.
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -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 3e64169ef527..38802d683969 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 */ |