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authorJan Kara <jack@suse.cz>2014-04-03 14:46:57 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-04-03 16:20:55 -0700
commit84d86f83f9d0e8431a3c9eae4c47e9d7ff49a411 (patch)
treef8708771a3316e70468d98691d14d1873ae69213 /fs/ocfs2/dlmglue.c
parente3a767b60fd8a9f5e133f42f4970cff77ec43173 (diff)
ocfs2: avoid blocking in ocfs2_mark_lockres_freeing() in downconvert thread
If we are dropping last inode reference from downconvert thread, we will end up calling ocfs2_mark_lockres_freeing() which can block if the lock we are freeing is queued thus creating an A-A deadlock. Luckily, since we are the downconvert thread, we can immediately dequeue the lock and thus avoid waiting in this case. Signed-off-by: Jan Kara <jack@suse.cz> Reviewed-by: Mark Fasheh <mfasheh@suse.de> Reviewed-by: Srinivas Eeda <srinivas.eeda@oracle.com> Cc: Joel Becker <jlbec@evilplan.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/ocfs2/dlmglue.c')
-rw-r--r--fs/ocfs2/dlmglue.c44
1 files changed, 41 insertions, 3 deletions
diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
index 19986959d149..6bd690b5a061 100644
--- a/fs/ocfs2/dlmglue.c
+++ b/fs/ocfs2/dlmglue.c
@@ -3144,22 +3144,60 @@ out:
return 0;
}
+static void ocfs2_process_blocked_lock(struct ocfs2_super *osb,
+ struct ocfs2_lock_res *lockres);
+
/* Mark the lockres as being dropped. It will no longer be
* queued if blocking, but we still may have to wait on it
* being dequeued from the downconvert thread before we can consider
* it safe to drop.
*
* You can *not* attempt to call cluster_lock on this lockres anymore. */
-void ocfs2_mark_lockres_freeing(struct ocfs2_lock_res *lockres)
+void ocfs2_mark_lockres_freeing(struct ocfs2_super *osb,
+ struct ocfs2_lock_res *lockres)
{
int status;
struct ocfs2_mask_waiter mw;
- unsigned long flags;
+ unsigned long flags, flags2;
ocfs2_init_mask_waiter(&mw);
spin_lock_irqsave(&lockres->l_lock, flags);
lockres->l_flags |= OCFS2_LOCK_FREEING;
+ if (lockres->l_flags & OCFS2_LOCK_QUEUED && current == osb->dc_task) {
+ /*
+ * We know the downconvert is queued but not in progress
+ * because we are the downconvert thread and processing
+ * different lock. So we can just remove the lock from the
+ * queue. This is not only an optimization but also a way
+ * to avoid the following deadlock:
+ * ocfs2_dentry_post_unlock()
+ * ocfs2_dentry_lock_put()
+ * ocfs2_drop_dentry_lock()
+ * iput()
+ * ocfs2_evict_inode()
+ * ocfs2_clear_inode()
+ * ocfs2_mark_lockres_freeing()
+ * ... blocks waiting for OCFS2_LOCK_QUEUED
+ * since we are the downconvert thread which
+ * should clear the flag.
+ */
+ spin_unlock_irqrestore(&lockres->l_lock, flags);
+ spin_lock_irqsave(&osb->dc_task_lock, flags2);
+ list_del_init(&lockres->l_blocked_list);
+ osb->blocked_lock_count--;
+ spin_unlock_irqrestore(&osb->dc_task_lock, flags2);
+ /*
+ * Warn if we recurse into another post_unlock call. Strictly
+ * speaking it isn't a problem but we need to be careful if
+ * that happens (stack overflow, deadlocks, ...) so warn if
+ * ocfs2 grows a path for which this can happen.
+ */
+ WARN_ON_ONCE(lockres->l_ops->post_unlock);
+ /* Since the lock is freeing we don't do much in the fn below */
+ ocfs2_process_blocked_lock(osb, lockres);
+ return;
+ }
while (lockres->l_flags & OCFS2_LOCK_QUEUED) {
lockres_add_mask_waiter(lockres, &mw, OCFS2_LOCK_QUEUED, 0);
spin_unlock_irqrestore(&lockres->l_lock, flags);
@@ -3180,7 +3218,7 @@ void ocfs2_simple_drop_lockres(struct ocfs2_super *osb,
{
int ret;
- ocfs2_mark_lockres_freeing(lockres);
+ ocfs2_mark_lockres_freeing(osb, lockres);
ret = ocfs2_drop_lock(osb, lockres);
if (ret)
mlog_errno(ret);