From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: Tejun Heo <tj@kernel.org>
Cc: Bart Van Assche <bvanassche@acm.org>,
syzbot <syzbot+831661966588c802aae9@syzkaller.appspotmail.com>,
jgg@ziepe.ca, linux-kernel@vger.kernel.org,
linux-rdma@vger.kernel.org, syzkaller-bugs@googlegroups.com,
Lai Jiangshan <jiangshanlai@gmail.com>
Subject: Re: [syzbot] possible deadlock in worker_thread
Date: Tue, 15 Feb 2022 19:26:18 +0900 [thread overview]
Message-ID: <a07e464c-69c6-6165-e88c-5a2eded79138@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <YgqSsuSN5C7StvKx@slm.duckdns.org>
On 2022/02/15 2:34, Tejun Heo wrote:
>
> Instead of doing the above, please add a wq flag to mark system wqs and
> trigger the warning that way and I'd leave it regardless of PROVE_LOCKING.
>
Do you mean something like below?
I think the above is easier to understand (for developers) because
The above prints variable's name (one of 'system_wq', 'system_highpri_wq',
'system_long_wq', 'system_unbound_wq', 'system_freezable_wq', 'system_power_efficient_wq'
or 'system_freezable_power_efficient_wq') with backtrace (which will be translated into
filename:line format) while the below prints queue's name (one of 'events', 'events_highpri',
'events_long', 'events_unbound', 'events_freezable', 'events_power_efficient' or
'events_freezable_power_efficient'). If CONFIG_KALLSYMS_ALL=y, we can print
variable's name using "%ps", but CONFIG_KALLSYMS_ALL is not always enabled.
The flag must not be used by user-defined WQs, for destroy_workqueue() involves
flush_workqueue(). If this flag is by error used on user-defined WQs, pointless
warning will be printed. I didn't pass this flag when creating system-wide WQs
because some developer might copy&paste the
system_wq = alloc_workqueue("events", 0, 0);
lines when converting.
---
include/linux/workqueue.h | 1 +
kernel/workqueue.c | 24 ++++++++++++++++++++++++
2 files changed, 25 insertions(+)
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 7fee9b6cfede..9e33dcd417d3 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -339,6 +339,7 @@ enum {
__WQ_ORDERED = 1 << 17, /* internal: workqueue is ordered */
__WQ_LEGACY = 1 << 18, /* internal: create*_workqueue() */
__WQ_ORDERED_EXPLICIT = 1 << 19, /* internal: alloc_ordered_workqueue() */
+ __WQ_SYSTEM_WIDE = 1 << 20, /* interbal: don't flush this workqueue */
WQ_MAX_ACTIVE = 512, /* I like 512, better ideas? */
WQ_MAX_UNBOUND_PER_CPU = 4, /* 4 * #cpus for unbound wq */
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 33f1106b4f99..dbb9c6bb54a7 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2805,6 +2805,21 @@ static bool flush_workqueue_prep_pwqs(struct workqueue_struct *wq,
return wait;
}
+static void warn_if_flushing_global_workqueue(struct workqueue_struct *wq)
+{
+ static DEFINE_RATELIMIT_STATE(flush_warn_rs, 600 * HZ, 1);
+
+ if (likely(!(wq->flags & __WQ_SYSTEM_WIDE)))
+ return;
+
+ ratelimit_set_flags(&flush_warn_rs, RATELIMIT_MSG_ON_RELEASE);
+ if (!__ratelimit(&flush_warn_rs))
+ return;
+ pr_warn("Since system-wide WQ is shared, flushing system-wide WQ can introduce unexpected locking dependency. Please replace %s usage in your code with your local WQ.\n",
+ wq->name);
+ dump_stack();
+}
+
/**
* flush_workqueue - ensure that any scheduled work has run to completion.
* @wq: workqueue to flush
@@ -2824,6 +2839,8 @@ void flush_workqueue(struct workqueue_struct *wq)
if (WARN_ON(!wq_online))
return;
+ warn_if_flushing_global_workqueue(wq);
+
lock_map_acquire(&wq->lockdep_map);
lock_map_release(&wq->lockdep_map);
@@ -6070,6 +6087,13 @@ void __init workqueue_init_early(void)
!system_unbound_wq || !system_freezable_wq ||
!system_power_efficient_wq ||
!system_freezable_power_efficient_wq);
+ system_wq->flags |= __WQ_SYSTEM_WIDE;
+ system_highpri_wq->flags |= __WQ_SYSTEM_WIDE;
+ system_long_wq->flags |= __WQ_SYSTEM_WIDE;
+ system_unbound_wq->flags |= __WQ_SYSTEM_WIDE;
+ system_freezable_wq->flags |= __WQ_SYSTEM_WIDE;
+ system_power_efficient_wq->flags |= __WQ_SYSTEM_WIDE;
+ system_freezable_power_efficient_wq->flags |= __WQ_SYSTEM_WIDE;
}
/**
--
2.32.0
next prev parent reply other threads:[~2022-02-15 10:26 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-10 19:27 [syzbot] possible deadlock in worker_thread syzbot
2022-02-11 18:59 ` Bart Van Assche
2022-02-12 5:31 ` Tetsuo Handa
2022-02-12 16:37 ` Bart Van Assche
2022-02-12 17:14 ` Tetsuo Handa
2022-02-13 15:33 ` Leon Romanovsky
2022-02-13 23:06 ` Bart Van Assche
2022-02-14 1:08 ` Tetsuo Handa
2022-02-14 3:44 ` Tejun Heo
2022-02-14 13:36 ` Tetsuo Handa
2022-02-14 17:34 ` Tejun Heo
2022-02-15 10:26 ` Tetsuo Handa [this message]
2022-02-15 10:43 ` Haakon Bugge
2022-02-15 12:48 ` Tetsuo Handa
2022-02-15 17:05 ` Bart Van Assche
2022-02-15 22:05 ` Tetsuo Handa
2022-02-22 18:26 ` Tejun Heo
2022-02-17 11:22 ` [PATCH v2] workqueue: Warn flush attempt using system-wide workqueues Tetsuo Handa
2022-02-22 18:36 ` Tejun Heo
[not found] ` <CGME20220223212048eucas1p1fab5e35ff398eff57808a8f1125dd15f@eucas1p1.samsung.com>
2022-02-23 21:20 ` Marek Szyprowski
2022-02-23 21:35 ` Tejun Heo
2022-02-23 22:06 ` Tetsuo Handa
2022-02-17 12:27 ` [syzbot] possible deadlock in worker_thread Fabio M. De Francesco
2022-02-22 18:30 ` Tejun Heo
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=a07e464c-69c6-6165-e88c-5a2eded79138@I-love.SAKURA.ne.jp \
--to=penguin-kernel@i-love.sakura.ne.jp \
--cc=bvanassche@acm.org \
--cc=jgg@ziepe.ca \
--cc=jiangshanlai@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-rdma@vger.kernel.org \
--cc=syzbot+831661966588c802aae9@syzkaller.appspotmail.com \
--cc=syzkaller-bugs@googlegroups.com \
--cc=tj@kernel.org \
/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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).