linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Waiman Long <longman@redhat.com>
To: David Laight <David.Laight@ACULAB.COM>,
	Peter Zijlstra <peterz@infradead.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
	Jann Horn <jannh@google.com>,
	Vasiliy Kulikov <segoon@openwall.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Bernd Edlinger <bernd.edlinger@hotmail.de>,
	Oleg Nesterov <oleg@redhat.com>,
	Christopher Yeoh <cyeoh@au1.ibm.com>,
	Cyrill Gorcunov <gorcunov@gmail.com>,
	Sargun Dhillon <sargun@sargun.me>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Arnaldo Carvalho de Melo <acme@kernel.org>
Subject: Re: [PATCH 2/3] rwsem: Implement down_read_interruptible
Date: Tue, 8 Dec 2020 10:34:27 -0500	[thread overview]
Message-ID: <edfd0eb8-192e-60be-f0ca-2a72a26caa07@redhat.com> (raw)
In-Reply-To: <71db845efc7d44b5a7d23b0e55b3a496@AcuMS.aculab.com>

On 12/8/20 4:12 AM, David Laight wrote:
> From: Waiman Long
>> Sent: 07 December 2020 19:02
> ...
>>> How much more difficult would it be to also add a timeout option?
>>> I looked at adding one to the mutex code - and fell into a big pile
>>> of replicated code.
>>>
>>> ISTM that one the initial locked exchange (and spin) fails a few
>>> extra instructions when heading for the sleep don't really matter
>>>
>> Actually, I had tried that before. See
>>
>> https://lore.kernel.org/lkml/20190911150537.19527-1-longman@redhat.com/
>>
>> That is for rwsem, but the same can be done for mutex. However, Peter
>> didn't seem to like the idea of a timeout parameter. Anyway, it is
>> certainly doable if there is a good use case for it.
> 'Unfortunately' my use-case if for an out-of-tree driver.
>
> The problem I was solving is a status call blocking because
> some other code is 'stuck' (probably an oops) with a mutex held.
>
> The code used to use down_timeout() (it was written for 2.4).
> When I changed to mutex_(to get optimistic spinning) I lost
> the ability to do the timeouts.

The primary reason for sending out that patchset was to work around some 
circular locking problem in existing code even though these circular 
locking scenarios are not likely to happen. Your case is certainly 
another potential circular locking problem as well.

Cheers,
Longman



  parent reply	other threads:[~2020-12-08 15:36 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-03 20:09 [PATCH 0/3] exec: Transform exec_update_mutex into a rw_semaphore Eric W. Biederman
2020-12-03 20:10 ` [PATCH 1/3] rwsem: Implement down_read_killable_nested Eric W. Biederman
2020-12-04  1:58   ` Waiman Long
2020-12-09 18:38   ` [tip: locking/core] " tip-bot2 for Eric W. Biederman
2020-12-03 20:11 ` [PATCH 2/3] rwsem: Implement down_read_interruptible Eric W. Biederman
2020-12-04  1:59   ` Waiman Long
2020-12-07  9:02     ` Peter Zijlstra
2020-12-07 15:33       ` Waiman Long
2020-12-07 16:58         ` David Laight
2020-12-07 19:02           ` Waiman Long
2020-12-08  9:12             ` David Laight
2020-12-08 12:32               ` Peter Zijlstra
2020-12-08 13:13                 ` David Laight
2020-12-08 15:34               ` Waiman Long [this message]
2020-12-08 16:23                 ` David Laight
2020-12-07 15:56       ` Eric W. Biederman
2020-12-08 14:52         ` Peter Zijlstra
2020-12-08 18:27           ` Eric W. Biederman
2020-12-09 18:36             ` Peter Zijlstra
2020-12-10 19:33               ` Eric W. Biederman
2020-12-11  8:16                 ` Peter Zijlstra
2020-12-09 18:38       ` [tip: locking/core] locking/rwsem: Introduce rwsem_write_trylock() tip-bot2 for Peter Zijlstra
2020-12-09 18:38       ` [tip: locking/core] locking/rwsem: Fold __down_{read,write}*() tip-bot2 for Peter Zijlstra
2020-12-09 18:38       ` [tip: locking/core] locking/rwsem: Better collate rwsem_read_trylock() tip-bot2 for Peter Zijlstra
2020-12-09 18:38   ` [tip: locking/core] rwsem: Implement down_read_interruptible tip-bot2 for Eric W. Biederman
2020-12-03 20:12 ` [PATCH 3/3] exec: Transform exec_update_mutex into a rw_semaphore Eric W. Biederman
2020-12-04 16:08   ` Bernd Edlinger
2020-12-04 17:21     ` Linus Torvalds
2020-12-04 19:34       ` Eric W. Biederman
2020-12-04 20:10         ` Linus Torvalds
2020-12-04 20:30           ` Bernd Edlinger
2020-12-04 20:48             ` Linus Torvalds
2020-12-04 21:48               ` Davidlohr Bueso
2020-12-05 18:05                 ` Eric W. Biederman
2020-12-07  9:15                   ` Peter Zijlstra
2020-12-07  9:09               ` Peter Zijlstra
2020-12-07 18:40                 ` Linus Torvalds
2020-12-08  8:34                   ` [PATCH] perf: Break deadlock involving exec_update_mutex Peter Zijlstra
2020-12-08 18:37                     ` Linus Torvalds
2020-12-10 18:38                     ` Davidlohr Bueso
2020-12-10 19:40                       ` Eric W. Biederman
2020-12-05 17:43           ` [PATCH 3/3] exec: Transform exec_update_mutex into a rw_semaphore Eric W. Biederman
2020-12-04 17:39     ` Eric W. Biederman
2020-12-03 22:42 ` [PATCH 0/3] " Linus Torvalds
2020-12-04  1:56   ` Waiman Long
2020-12-04  4:54   ` Davidlohr Bueso

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=edfd0eb8-192e-60be-f0ca-2a72a26caa07@redhat.com \
    --to=longman@redhat.com \
    --cc=David.Laight@ACULAB.COM \
    --cc=acme@kernel.org \
    --cc=arnd@arndb.de \
    --cc=bernd.edlinger@hotmail.de \
    --cc=christian.brauner@ubuntu.com \
    --cc=cyeoh@au1.ibm.com \
    --cc=ebiederm@xmission.com \
    --cc=gorcunov@gmail.com \
    --cc=jannh@google.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=oleg@redhat.com \
    --cc=peterz@infradead.org \
    --cc=sargun@sargun.me \
    --cc=segoon@openwall.com \
    --cc=torvalds@linux-foundation.org \
    --cc=viro@zeniv.linux.org.uk \
    --cc=will@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).