From: Oleg Nesterov <oleg@redhat.com>
To: Al Viro <viro@zeniv.linux.org.uk>,
Dave Chinner <david@fromorbit.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Jan Kara <jack@suse.cz>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Peter Zijlstra <peterz@infradead.org>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2 3/8] document rwsem_release() in sb_wait_write()
Date: Tue, 11 Aug 2015 19:04:04 +0200 [thread overview]
Message-ID: <20150811170404.GA26911@redhat.com> (raw)
In-Reply-To: <20150811170343.GA26881@redhat.com>
Not only we need to avoid the warning from lockdep_sys_exit(), the
caller of freeze_super() can never release this lock. Another thread
can do this, so there is another reason for rwsem_release().
Plus the comment should explain why we have to fool lockdep.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
fs/super.c | 12 +++++++++---
1 files changed, 9 insertions(+), 3 deletions(-)
diff --git a/fs/super.c b/fs/super.c
index d0fdd49..89b58fb 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1236,11 +1236,17 @@ static void sb_wait_write(struct super_block *sb, int level)
{
s64 writers;
+ rwsem_acquire(&sb->s_writers.lock_map[level-1], 0, 0, _THIS_IP_);
/*
- * We just cycle-through lockdep here so that it does not complain
- * about returning with lock to userspace
+ * We are going to return to userspace and forget about this lock, the
+ * ownership goes to the caller of thaw_super() which does unlock.
+ *
+ * FIXME: we should do this before return from freeze_super() after we
+ * called sync_filesystem(sb) and s_op->freeze_fs(sb), and thaw_super()
+ * should re-acquire these locks before s_op->unfreeze_fs(sb). However
+ * this leads to lockdep false-positives, so currently we do the early
+ * release right after acquire.
*/
- rwsem_acquire(&sb->s_writers.lock_map[level-1], 0, 0, _THIS_IP_);
rwsem_release(&sb->s_writers.lock_map[level-1], 1, _THIS_IP_);
do {
--
1.5.5.1
next prev parent reply other threads:[~2015-08-11 17:07 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-11 17:03 [PATCH v2 0/8] change sb_writers to use percpu_rw_semaphore Oleg Nesterov
2015-08-11 17:03 ` [PATCH v2 1/8] introduce __sb_{acquire,release}_write() helpers Oleg Nesterov
2015-08-13 9:45 ` Jan Kara
2015-08-13 9:56 ` Jan Kara
2015-08-13 13:17 ` Oleg Nesterov
2015-08-13 13:32 ` Jan Kara
2015-08-13 13:37 ` Oleg Nesterov
2015-08-11 17:04 ` [PATCH v2 2/8] fix the broken lockdep logic in __sb_start_write() Oleg Nesterov
2015-08-13 10:02 ` Jan Kara
2015-08-13 13:22 ` Oleg Nesterov
2015-08-13 13:29 ` Jan Kara
2015-08-11 17:04 ` Oleg Nesterov [this message]
2015-08-13 10:22 ` [PATCH v2 3/8] document rwsem_release() in sb_wait_write() Jan Kara
2015-08-11 17:04 ` [PATCH v2 4/8] percpu-rwsem: introduce percpu_down_read_trylock() Oleg Nesterov
2015-08-11 17:04 ` [PATCH v2 5/8] percpu-rwsem: introduce percpu_rwsem_release() and percpu_rwsem_acquire() Oleg Nesterov
2015-08-11 17:04 ` [PATCH v2 6/8] percpu-rwsem: kill CONFIG_PERCPU_RWSEM Oleg Nesterov
2015-08-11 17:04 ` [PATCH v2 7/8] shift percpu_counter_destroy() into destroy_super_work() Oleg Nesterov
2015-08-13 10:35 ` Jan Kara
2015-08-13 13:36 ` Oleg Nesterov
2015-08-13 14:09 ` Jan Kara
2015-08-13 15:20 ` Oleg Nesterov
2015-08-11 17:04 ` [PATCH v2 8/8] change sb_writers to use percpu_rw_semaphore Oleg Nesterov
2015-08-13 10:48 ` Jan Kara
2015-08-12 13:11 ` [PATCH v2 9/8] don't fool lockdep in freeze_super() and thaw_super() paths Oleg Nesterov
2015-08-13 11:01 ` Jan Kara
2015-08-13 13:58 ` Oleg Nesterov
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