From: Johannes Berg <johannes@sipsolutions.net>
To: paulmck@linux.vnet.ibm.com
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Nicolai Stange <nicstange@gmail.com>,
gregkh <gregkh@linuxfoundation.org>,
sharon.dvir@intel.com, Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
linux-wireless <linux-wireless@vger.kernel.org>
Subject: Re: deadlock in synchronize_srcu() in debugfs?
Date: Mon, 27 Mar 2017 13:18:22 +0200 [thread overview]
Message-ID: <1490613502.3393.2.camel@sipsolutions.net> (raw)
In-Reply-To: <20170324202033.GA24098@linux.vnet.ibm.com>
On Fri, 2017-03-24 at 13:20 -0700, Paul E. McKenney wrote:
>
> And I cannot resist adding this one:
>
> CPU 1 CPU 2
> i = srcu_read_lock(&s1); mutex_lock(&l1);
> mutex_lock(&l1); synchronize_srcu(&s2);
> mutex_unlock(&l1); mutex_unlock(&l1);
> srcu_read_unlock(&s1, i);
>
> CPU 3 CPU 4
> i = srcu_read_lock(&s2); mutex_lock(&l2);
> mutex_lock(&l2); synchronize_srcu(&s1);
> mutex_unlock(&l2); mutex_unlock(&l2);
> srcu_read_unlock(&s2, i);
>
> Removing the SRCU statements from any of these CPU would break the
> deadlock. This can be easily extended to a deadlock cycle involving
> any number of srcu_struct structures.
>
> But this would still be a cycle involving an srcu_read_lock() and a
> synchronize_srcu() on the same srcu_struct, which is reassuring.
Right, you can cycle this indefinitely. lockdep has some kind of
maximum chain length I think. :)
johannes
next prev parent reply other threads:[~2017-03-27 11:18 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 [this message]
2017-03-23 15:36 ` Nicolai Stange
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1490613502.3393.2.camel@sipsolutions.net \
--to=johannes@sipsolutions.net \
--cc=gregkh@linuxfoundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-wireless@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=nicstange@gmail.com \
--cc=paulmck@linux.vnet.ibm.com \
--cc=peterz@infradead.org \
--cc=sharon.dvir@intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.