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From: Nicolai Stange <nicstange@gmail.com>
To: Johannes Berg <johannes@sipsolutions.net>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
	Nicolai Stange <nicstange@gmail.com>,
	"Paul E.McKenney" <paulmck@linux.vnet.ibm.com>,
	gregkh <gregkh@linuxfoundation.org>
Subject: Re: deadlock in synchronize_srcu() in debugfs?
Date: Thu, 23 Mar 2017 16:36:19 +0100	[thread overview]
Message-ID: <87o9ws6m4s.fsf@gmail.com> (raw)
In-Reply-To: <1490280886.2766.4.camel@sipsolutions.net> (Johannes Berg's message of "Thu, 23 Mar 2017 15:54:46 +0100")

Hi Johannes,

On Thu, Mar 23 2017, Johannes Berg wrote:

> Before I go hunting - has anyone seen a deadlock in synchronize_srcu()
> in debugfs_remove() before?

Not yet. How reproducible is this?


> We're observing that with our (backported, but very recent) driver
> against 4.9 (and 4.10, I think),

Do I understand it correctly that this driver has been backported from
4.11-rcX to 4.9/10 and that there isn't any issue with 4.11-rcX?


> but there are no backports of any debugfs things so the backport
> itself doesn't seem like a likely problem.

Right, there haven't been any SRCU related changes to debugfs after
4.8.


> sysrq-w shows a lot of tasks blocked on various locks (e.g. RTNL), but
> the ultimate problem is the wireless stack getting blocked on
> debugfs_remove_recursive(), in __synchronize_srcu(), in
> wait_for_completion() (while holding lots of locks, hence the other
> tasks getting stuck).

Could you share a complete backtrace? For example, is the
debugfs_remove_recursive() called from any debugfs file's fops and thus,
possibly from within a SRCU read side critical section?


Thanks,

Nicolai

  parent reply	other threads:[~2017-03-23 15:36 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-23 14:54 deadlock in synchronize_srcu() in debugfs? Johannes Berg
2017-03-23 15:29 ` Johannes Berg
2017-03-24  8:56   ` Johannes Berg
2017-03-24  9:24     ` Johannes Berg
2017-03-24 17:45       ` Paul E. McKenney
2017-03-24 18:51         ` Johannes Berg
2017-03-24 19:33           ` Paul E. McKenney
2017-03-24 20:20             ` Paul E. McKenney
2017-03-27 11:18               ` Johannes Berg
2017-03-23 15:36 ` Nicolai Stange [this message]
2017-03-23 15:47   ` Johannes Berg
2017-03-27 11:36   ` Johannes Berg
2017-03-30  7:32     ` Nicolai Stange
2017-03-30  7:55       ` Johannes Berg
2017-03-30 10:27         ` Nicolai Stange
2017-03-30 11:11           ` Johannes Berg
2017-03-31  9:03             ` Nicolai Stange
2017-03-31  9:44               ` Johannes Berg
2017-04-16  9:51               ` [RFC PATCH 0/9] debugfs: per-file removal protection Nicolai Stange
2017-04-16  9:51                 ` [RFC PATCH 1/9] debugfs: add support for more elaborate ->d_fsdata Nicolai Stange
2017-04-16  9:51                 ` [RFC PATCH 2/9] debugfs: implement per-file removal protection Nicolai Stange
2017-04-18  2:23                   ` [lkp-robot] [debugfs] f3e7155d08: BUG:unable_to_handle_kernel kernel test robot
2017-04-18  2:23                     ` kernel test robot
2017-04-23 18:37                     ` Nicolai Stange
2017-04-23 18:37                       ` Nicolai Stange
2017-04-24  6:36                       ` Ye Xiaolong
2017-04-24  6:36                         ` Ye Xiaolong
2017-04-16  9:51                 ` [RFC PATCH 3/9] debugfs: debugfs_real_fops(): drop __must_hold sparse annotation Nicolai Stange
2017-04-16  9:51                 ` [RFC PATCH 4/9] debugfs: convert to debugfs_file_get() and -put() Nicolai Stange
2017-04-16  9:51                 ` [RFC PATCH 5/9] IB/hfi1: " Nicolai Stange
2017-04-16  9:51                 ` [RFC PATCH 6/9] debugfs: purge obsolete SRCU based removal protection Nicolai Stange
2017-04-16  9:51                 ` [RFC PATCH 7/9] debugfs: call debugfs_real_fops() only after debugfs_file_get() Nicolai Stange
2017-04-16  9:51                 ` [RFC PATCH 8/9] debugfs: defer debugfs_fsdata allocation to first usage Nicolai Stange
2017-04-18  9:36                   ` Johannes Berg
2017-05-02 20:05                     ` Nicolai Stange
2017-05-03  5:43                       ` Johannes Berg
2017-04-16  9:51                 ` [RFC PATCH 9/9] debugfs: free debugfs_fsdata instances Nicolai Stange
2017-04-17 16:01                   ` Paul E. McKenney
2017-04-18  9:39                     ` Johannes Berg
2017-04-18 13:31                       ` Paul E. McKenney
2017-04-18 13:40                         ` Johannes Berg
2017-04-18 15:17                           ` Paul E. McKenney
2017-04-18 15:20                             ` Johannes Berg
2017-04-18 17:19                               ` Paul E. McKenney
2017-03-23 15:37 ` deadlock in synchronize_srcu() in debugfs? Paul E. McKenney
2017-03-23 15:46   ` Johannes Berg

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