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From: Jan Kara <jack@suse.cz>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
	Dave Chinner <david@fromorbit.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Jan Kara <jack@suse.cz>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/8] document rwsem_release() in sb_wait_write()
Date: Thu, 13 Aug 2015 12:22:19 +0200	[thread overview]
Message-ID: <20150813102219.GF26599@quack.suse.cz> (raw)
In-Reply-To: <20150811170404.GA26911@redhat.com>

On Tue 11-08-15 19:04:04, Oleg Nesterov wrote:
> 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>

Looks good. You can add:

Reviewed-by: Jan Kara <jack@suse.com>

								Honza

> ---
>  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
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

  reply	other threads:[~2015-08-13 10:22 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 ` [PATCH v2 3/8] document rwsem_release() in sb_wait_write() Oleg Nesterov
2015-08-13 10:22   ` Jan Kara [this message]
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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