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From: Luis Chamberlain <mcgrof@kernel.org>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Ming Lei <ming.lei@redhat.com>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	tj@kernel.org, akpm@linux-foundation.org, minchan@kernel.org,
	jeyu@kernel.org, shuah@kernel.org, bvanassche@acm.org,
	dan.j.williams@intel.com, joe@perches.com, tglx@linutronix.de,
	keescook@chromium.org, rostedt@goodmis.org,
	linux-spdx@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v8 11/12] zram: fix crashes with cpu hotplug multistate
Date: Tue, 19 Oct 2021 12:46:29 -0700	[thread overview]
Message-ID: <YW8glVdremhn1eF2@bombadil.infradead.org> (raw)
In-Reply-To: <YW8AQ4fMNV8MT1vX@kroah.com>

On Tue, Oct 19, 2021 at 07:28:35PM +0200, Greg KH wrote:
> On Tue, Oct 19, 2021 at 09:30:05AM -0700, Luis Chamberlain wrote:
> > On Tue, Oct 19, 2021 at 06:25:18PM +0200, Greg KH wrote:
> > > On Tue, Oct 19, 2021 at 08:50:24AM -0700, Luis Chamberlain wrote:
> > > > So do you want to take the position:
> > > > 
> > > > Hey driver authors: you cannot use any shared lock on module removal and
> > > > on sysfs ops?
> > > 
> > > Yes, I would not recommend using such a lock at all.  sysfs operations
> > > happen on a per-device basis, so you can lock the device structure.
> > 
> > All devices are going to be removed on module removal and so cannot be locked.
> 
> devices are not normally created by a driver, that is up to the bus
> controller logic.  A module will just disconnect itself from the device,
> the device does not go away.
> 
> But yes, there are exceptions, and if you are doing something odd like
> that, then you need to be aware of crazy things like this, so be
> careful.  But for all normal drivers, they do not have to worry about
> this.

"Recommend" is a weak position to take given a possible deadlock with sysfs.

Do we want to at the very least document this is not a supported scheme?

If so I can also add a simple 1 level indirrection coccinelle patch to
detect these schemes and complain about them as wel, if we are going to
take this position.

But to simply disregard this as "not an issue", or we won't do anything
seems pretty counter productive given we *do* had drivers with this
issue before *and* still have them upstream, and can end up with more
drivers like this later.

  Luis

  reply	other threads:[~2021-10-19 19:46 UTC|newest]

Thread overview: 94+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-27 16:37 [PATCH v8 00/12] syfs: generic deadlock fix with module removal Luis Chamberlain
2021-09-27 16:37 ` [PATCH v8 01/12] LICENSES: Add the copyleft-next-0.3.1 license Luis Chamberlain
     [not found]   ` <202110050907.35FBD2A1@keescook>
     [not found]     ` <YWR2ZrtzChamY1y4@bombadil.infradead.org>
2021-10-11 17:57       ` Kees Cook
2021-09-27 16:37 ` [PATCH v8 02/12] testing: use the copyleft-next-0.3.1 SPDX tag Luis Chamberlain
2021-10-05 16:11   ` Kees Cook
2021-09-27 16:37 ` [PATCH v8 03/12] selftests: add tests_sysfs module Luis Chamberlain
2021-10-05 14:16   ` Greg KH
2021-10-05 16:57     ` Tim.Bird
2021-10-11 17:40       ` Luis Chamberlain
2021-10-11 17:38     ` Luis Chamberlain
2021-10-07 14:23   ` Miroslav Benes
2021-10-11 19:11     ` Luis Chamberlain
     [not found]   ` <202110050912.3DF681ED@keescook>
2021-10-11 19:03     ` Luis Chamberlain
2021-09-27 16:37 ` [PATCH v8 04/12] kernfs: add initial failure injection support Luis Chamberlain
2021-10-05 19:47   ` Kees Cook
2021-10-11 20:44     ` Luis Chamberlain
2021-09-27 16:37 ` [PATCH v8 05/12] test_sysfs: add support to use kernfs failure injection Luis Chamberlain
2021-10-05 19:51   ` Kees Cook
2021-10-11 20:56     ` Luis Chamberlain
2021-09-27 16:37 ` [PATCH v8 06/12] kernel/module: add documentation for try_module_get() Luis Chamberlain
2021-10-05 19:58   ` Kees Cook
2021-10-11 21:16     ` Luis Chamberlain
2021-09-27 16:38 ` [PATCH v8 07/12] fs/kernfs/symlink.c: replace S_IRWXUGO with 0777 on kernfs_create_link() Luis Chamberlain
2021-10-05 19:59   ` Kees Cook
2021-09-27 16:38 ` [PATCH v8 08/12] fs/sysfs/dir.c: replace S_IRWXU|S_IRUGO|S_IXUGO with 0755 sysfs_create_dir_ns() Luis Chamberlain
2021-10-05 16:05   ` Kees Cook
2021-09-27 16:38 ` [PATCH v8 09/12] sysfs: fix deadlock race with module removal Luis Chamberlain
2021-10-05  9:24   ` Ming Lei
2021-10-11 21:25     ` Luis Chamberlain
2021-10-12  0:20       ` Ming Lei
2021-10-12 21:18         ` Luis Chamberlain
2021-10-13  1:07           ` Ming Lei
2021-10-13 12:35             ` Luis Chamberlain
2021-10-13 15:04               ` Ming Lei
2021-10-13 21:16                 ` Luis Chamberlain
2021-10-05 20:50   ` Kees Cook
2021-10-11 22:26     ` Luis Chamberlain
2021-10-13 12:41       ` Luis Chamberlain
2021-09-27 16:38 ` [PATCH v8 10/12] test_sysfs: enable deadlock tests by default Luis Chamberlain
2021-09-27 16:38 ` [PATCH v8 11/12] zram: fix crashes with cpu hotplug multistate Luis Chamberlain
2021-10-05 20:55   ` Kees Cook
2021-10-11 18:27     ` Luis Chamberlain
2021-10-14  1:55   ` Ming Lei
2021-10-14  2:11     ` Ming Lei
2021-10-14 20:24       ` Luis Chamberlain
2021-10-14 23:52         ` Ming Lei
2021-10-15  0:22           ` Luis Chamberlain
2021-10-15  8:36             ` Ming Lei
2021-10-15  8:52               ` Greg KH
2021-10-15 17:31               ` Luis Chamberlain
2021-10-16 11:28                 ` Ming Lei
2021-10-18 19:32                   ` Luis Chamberlain
2021-10-19  2:34                     ` Ming Lei
2021-10-19  6:23                       ` Miroslav Benes
2021-10-19  9:23                         ` Ming Lei
2021-10-20  6:43                           ` Miroslav Benes
2021-10-20  7:49                             ` Ming Lei
2021-10-20  8:19                               ` Miroslav Benes
2021-10-20  8:28                                 ` Greg KH
2021-10-25  9:58                                   ` Miroslav Benes
2021-10-20 10:09                                 ` Ming Lei
2021-10-26  8:48                                   ` Petr Mladek
2021-10-26 15:37                                     ` Ming Lei
2021-10-26 17:01                                       ` Luis Chamberlain
2021-10-27 11:57                                         ` Miroslav Benes
2021-10-27 14:27                                           ` Luis Chamberlain
2021-11-02 15:24                                           ` Petr Mladek
2021-11-02 16:25                                             ` Luis Chamberlain
2021-11-03  0:01                                               ` Ming Lei
2021-11-03 12:44                                                 ` Luis Chamberlain
2021-10-27 11:42                                       ` Miroslav Benes
2021-11-02 14:15                                       ` Petr Mladek
2021-11-02 14:51                                         ` Petr Mladek
2021-11-02 15:17                                           ` Ming Lei
2021-11-02 14:56                                         ` Ming Lei
2021-10-19 15:28                       ` Luis Chamberlain
2021-10-19 16:29                         ` Ming Lei
2021-10-19 19:36                           ` Luis Chamberlain
2021-10-20  1:15                             ` Ming Lei
2021-10-20 15:48                               ` Luis Chamberlain
2021-10-21  0:39                                 ` Ming Lei
2021-10-21 17:18                                   ` Luis Chamberlain
2021-10-22  0:05                                     ` Ming Lei
2021-10-19 15:50                       ` Luis Chamberlain
2021-10-19 16:25                         ` Greg KH
2021-10-19 16:30                           ` Luis Chamberlain
2021-10-19 17:28                             ` Greg KH
2021-10-19 19:46                               ` Luis Chamberlain [this message]
2021-10-19 16:39                         ` Ming Lei
2021-10-19 19:38                           ` Luis Chamberlain
2021-10-20  0:55                             ` Ming Lei
2021-09-27 16:38 ` [PATCH v8 12/12] zram: use ATTRIBUTE_GROUPS to fix sysfs deadlock module removal Luis Chamberlain
2021-10-05 20:57   ` Kees Cook
2021-10-11 18:28     ` Luis Chamberlain

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