From: Alan Stern <stern@rowland.harvard.edu>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
USB list <linux-usb@vger.kernel.org>
Subject: Re: Converting dev->mutex into dev->spinlock ?
Date: Sat, 4 Feb 2023 10:40:52 -0500 [thread overview]
Message-ID: <Y958hOvtqq7Uiu0G@rowland.harvard.edu> (raw)
In-Reply-To: <e89ad942-cab6-fad1-1cc2-98885d829ea7@I-love.SAKURA.ne.jp>
On Sun, Feb 05, 2023 at 12:30:07AM +0900, Tetsuo Handa wrote:
> On 2023/02/05 0:12, Alan Stern wrote:
> >> it would solve many deadlocks in driver code if you can update
> >
> > What deadlocks? If there are so many deadlocks floating around in
> > driver code, why haven't we heard about them before now?
>
> Since dev->mutex is hidden from lockdep checks, nobody can see lockdep warnings.
> syzbot is reporting real deadlocks without lockdep warnings, for the fundamental
> problem you mentioned in https://lkml.kernel.org/r/Pine.LNX.4.44L0.0804171117450.18040-100000@iolanthe.rowland.org
> is remaining. I'm suggesting you that now is time to address this fundamental problem.
Maybe so. But the place to address it is inside lockdep, not in the
driver core.
> >> (by e.g. replacing dev->mutex with dev->spinlock and dev->atomic_flags).
> >> But I'm not familiar enough to propose such change...
> >
> > Such a change cannot be made. Consider this: Driver callbacks often
> > need to sleep. But when a thread holds a spinlock, it is not allowed to
> > sleep. Therefore driver callbacks must not be invoked while a spinlock
> > is held.
>
> What I'm suggesting is "Do not call driver callbacks with dev->mutex held,
> by rewriting driver core code".
That cannot be done. The only possible solution is to teach lockdep how
to handle recursive locking structures.
Alan Stern
prev parent reply other threads:[~2023-02-04 15:41 UTC|newest]
Thread overview: 75+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-04 13:32 Converting dev->mutex into dev->spinlock ? Tetsuo Handa
2023-02-04 13:47 ` Greg Kroah-Hartman
2023-02-04 14:21 ` Tetsuo Handa
2023-02-04 14:34 ` Greg Kroah-Hartman
2023-02-04 15:16 ` Tetsuo Handa
2023-02-04 15:34 ` Alan Stern
2023-02-04 16:12 ` Tetsuo Handa
2023-02-04 16:27 ` Alan Stern
2023-02-04 17:09 ` Tetsuo Handa
2023-02-04 20:01 ` Alan Stern
2023-02-04 20:14 ` Linus Torvalds
2023-02-05 1:23 ` Alan Stern
2023-02-06 14:13 ` Tetsuo Handa
2023-02-06 15:45 ` Alan Stern
2023-02-07 13:07 ` Tetsuo Handa
2023-02-07 17:46 ` Alan Stern
2023-02-07 22:17 ` Tetsuo Handa
2023-02-08 0:34 ` Alan Stern
[not found] ` <20230208080739.1649-1-hdanton@sina.com>
2023-02-08 10:30 ` [PATCH] drivers/core: Replace lockdep_set_novalidate_class() with unique class keys Tetsuo Handa
2023-02-08 15:07 ` Alan Stern
2023-02-09 0:22 ` Tetsuo Handa
2023-02-09 0:46 ` Linus Torvalds
2023-02-09 1:50 ` Tetsuo Handa
2023-02-09 2:26 ` Alan Stern
2023-02-11 2:04 ` Tetsuo Handa
2023-02-11 21:41 ` [PATCH RFC] " Alan Stern
2023-02-11 21:51 ` Linus Torvalds
2023-02-11 23:06 ` Kent Overstreet
2023-02-11 23:08 ` Kent Overstreet
2023-02-11 23:24 ` Kent Overstreet
2023-02-12 2:40 ` Alan Stern
2023-02-12 2:46 ` Kent Overstreet
2023-02-12 3:03 ` Alan Stern
2023-02-12 3:10 ` Kent Overstreet
2023-02-12 15:23 ` Alan Stern
2023-02-12 19:14 ` Kent Overstreet
2023-02-12 20:19 ` Alan Stern
2023-02-12 20:51 ` Kent Overstreet
2023-02-13 1:23 ` Alan Stern
2023-02-13 2:21 ` Kent Overstreet
2023-02-13 15:25 ` Alan Stern
2023-02-13 9:29 ` Peter Zijlstra
2023-02-13 9:27 ` Peter Zijlstra
2023-02-13 15:28 ` Alan Stern
2023-02-13 16:36 ` Peter Zijlstra
2023-02-13 9:24 ` Peter Zijlstra
2023-02-13 15:25 ` Alan Stern
2023-02-13 16:29 ` Peter Zijlstra
2023-02-14 1:51 ` Boqun Feng
2023-02-14 1:53 ` Boqun Feng
2023-02-14 2:03 ` Alan Stern
2023-02-14 2:09 ` Boqun Feng
[not found] ` <20230214052733.3354-1-hdanton@sina.com>
2023-02-14 5:55 ` Boqun Feng
2023-02-14 10:48 ` Peter Zijlstra
2023-02-14 16:22 ` Boqun Feng
2023-02-15 10:45 ` Peter Zijlstra
2023-02-20 17:32 ` Boqun Feng
2023-02-13 18:46 ` Kent Overstreet
2023-02-14 11:05 ` Peter Zijlstra
2023-02-14 20:05 ` Alan Stern
2023-02-15 10:33 ` Peter Zijlstra
2023-02-14 20:16 ` Kent Overstreet
[not found] ` <20230212013220.2678-1-hdanton@sina.com>
2023-02-12 1:52 ` Kent Overstreet
2023-02-13 9:49 ` Peter Zijlstra
2023-02-13 16:18 ` Alan Stern
2023-02-13 17:51 ` Greg Kroah-Hartman
2023-02-13 18:05 ` Alan Stern
2023-02-05 1:31 ` Converting dev->mutex into dev->spinlock ? Tetsuo Handa
2023-02-05 16:46 ` Alan Stern
[not found] ` <20230206025629.1786-1-hdanton@sina.com>
2023-02-06 4:44 ` Matthew Wilcox
2023-02-06 5:17 ` Greg Kroah-Hartman
[not found] ` <20230206064305.1838-1-hdanton@sina.com>
2023-02-06 6:48 ` Greg Kroah-Hartman
2023-02-04 15:12 ` Alan Stern
2023-02-04 15:30 ` Tetsuo Handa
2023-02-04 15:40 ` Alan Stern [this message]
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=Y958hOvtqq7Uiu0G@rowland.harvard.edu \
--to=stern@rowland.harvard.edu \
--cc=gregkh@linuxfoundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-usb@vger.kernel.org \
--cc=penguin-kernel@i-love.sakura.ne.jp \
--cc=rafael@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