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From: Luis Chamberlain <mcgrof@kernel.org>
To: Tejun Heo <tj@kernel.org>
Cc: gregkh@linuxfoundation.org, akpm@linux-foundation.org,
	minchan@kernel.org, jeyu@kernel.org, shuah@kernel.org,
	rdunlap@infradead.org, rafael@kernel.org, masahiroy@kernel.org,
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	copyleft-next@lists.fedorahosted.org
Subject: Re: [PATCH v7 09/12] sysfs: fix deadlock race with module removal
Date: Mon, 20 Sep 2021 12:38:05 -0700	[thread overview]
Message-ID: <YUjjHRHWCso1tjeX@bombadil.infradead.org> (raw)
In-Reply-To: <YUjfeGuSVVq84iHc@mtj.duckdns.org>

On Mon, Sep 20, 2021 at 09:22:32AM -1000, Tejun Heo wrote:
> On Mon, Sep 20, 2021 at 12:15:22PM -0700, Luis Chamberlain wrote:
> 
> > Right, the reason I mention the alternative is that we technically don't
> > need to use try in this case since during a kernfs op it is implied the
> > module will be pinned, but we have further motivations to use a try
> 
> I'm confused. If the module is already pinned, why are we getting an
> extra reference? 

Sorry, I meant its pinned implicitly not through an actual refcount. A module
exit can happen then in that case, it just that the sysfs removal will
have to wait until the active reference for the kernfs ops go down.

> Also, I don't understand how this has that much to do
> with preventing ddoses. I mean, it does cut down the duration of one
> operation but the eventual gating is through whoever acquiring the
> initial reference through try_module_get(), which again is the *only*
> way to acquire a fresh reference.

True. I can just leave that out from the commit log. But it is perhaps
an implicit gain here that using try alows module exit to trump use
of an kernfs op. Maybe's that's sufficient to mention.

  Luis

  reply	other threads:[~2021-09-21  1:41 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20210918050430.3671227-1-mcgrof@kernel.org>
2021-09-18  5:04 ` [PATCH v7 01/12] LICENSES: Add the copyleft-next-0.3.1 license Luis Chamberlain
2021-09-18  5:04 ` [PATCH v7 02/12] testing: use the copyleft-next-0.3.1 SPDX tag Luis Chamberlain
2021-09-18  5:04 ` [PATCH v7 03/12] selftests: add tests_sysfs module Luis Chamberlain
2021-09-20 21:38   ` Bart Van Assche
2021-09-18  5:04 ` [PATCH v7 04/12] kernfs: add initial failure injection support Luis Chamberlain
2021-09-18  5:04 ` [PATCH v7 05/12] test_sysfs: add support to use kernfs failure injection Luis Chamberlain
2021-09-18  5:04 ` [PATCH v7 06/12] kernel/module: add documentation for try_module_get() Luis Chamberlain
2021-09-18  5:04 ` [PATCH v7 07/12] fs/kernfs/symlink.c: replace S_IRWXUGO with 0777 on kernfs_create_link() Luis Chamberlain
2021-09-18  5:04 ` [PATCH v7 08/12] fs/sysfs/dir.c: replace S_IRWXU|S_IRUGO|S_IXUGO with 0755 sysfs_create_dir_ns() Luis Chamberlain
2021-09-18  5:04 ` [PATCH v7 09/12] sysfs: fix deadlock race with module removal Luis Chamberlain
2021-09-20 17:53   ` Tejun Heo
2021-09-20 19:15     ` Luis Chamberlain
2021-09-20 19:22       ` Tejun Heo
2021-09-20 19:38         ` Luis Chamberlain [this message]
2021-09-20 20:52   ` Dan Williams
2021-09-20 21:17     ` Luis Chamberlain
2021-09-20 21:55       ` Dan Williams
2021-09-21  0:03         ` Luis Chamberlain
2021-09-20 21:36   ` Bart Van Assche
2021-09-20 21:43     ` Luis Chamberlain
2021-09-18  5:04 ` [PATCH v7 10/12] test_sysfs: enable deadlock tests by default Luis Chamberlain
2021-09-18  5:04 ` [PATCH v7 11/12] zram: fix crashes with cpu hotplug multistate Luis Chamberlain
2021-09-18  5:04 ` [PATCH v7 12/12] zram: use ATTRIBUTE_GROUPS to fix sysfs deadlock module removal Luis Chamberlain
2021-09-20 17:55 ` [PATCH v7 00/12 (RESEND)] syfs: generic deadlock fix with " Tejun Heo
2021-09-27 15:11   ` Luis Chamberlain
     [not found] <20210917194709.3562413-1-mcgrof@kernel.org>
     [not found] ` <20210917194709.3562413-10-mcgrof@kernel.org>
     [not found]   ` <c70dcb03e27e43c5b5311e184357df39@AcuMS.aculab.com>
2021-09-21 15:48     ` [PATCH v7 09/12] sysfs: fix deadlock race " Luis Chamberlain

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