From: Tejun Heo <tj@kernel.org>
To: Luis Chamberlain <mcgrof@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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stephen@networkplumber.org, David.Laight@aculab.com,
bvanassche@acm.org, jolsa@kernel.org,
andriy.shevchenko@linux.intel.com, trishalfonso@google.com,
andreyknvl@gmail.com, jikos@kernel.org, mbenes@suse.com,
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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 09:22:32 -1000 [thread overview]
Message-ID: <YUjfeGuSVVq84iHc@mtj.duckdns.org> (raw)
In-Reply-To: <YUjdytEDkCughtSz@bombadil.infradead.org>
Hello,
On Mon, Sep 20, 2021 at 12:15:22PM -0700, Luis Chamberlain wrote:
> > I find this explanation odd because there's no real equivalent to locking
> > the module (as opposed to try locking)
>
> Actually there is, __module_get() but I suspect some of these users are
> probably incorrect and should be be moved to try. The documentation
__module_get() is just getting an extra ref when the caller already
has one (or more). It can't be used to freshly acquire a new
reference. There is no equivalence between the relationship between
try_module_get() and __module_get() and the one between spin_trylock()
and spin_lock().
> 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? 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.
Thanks.
--
tejun
next prev parent reply other threads:[~2021-09-21 2:53 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 [this message]
2021-09-20 19:38 ` Luis Chamberlain
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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