From: Luis Chamberlain <mcgrof@kernel.org>
To: Kees Cook <keescook@chromium.org>, akpm@linux-foundation.org
Cc: tj@kernel.org, gregkh@linuxfoundation.org, minchan@kernel.org,
jeyu@kernel.org, shuah@kernel.org, bvanassche@acm.org,
dan.j.williams@intel.com, joe@perches.com, tglx@linutronix.de,
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: Mon, 11 Oct 2021 11:27:30 -0700 [thread overview]
Message-ID: <YWSCEs8BE8HF/+Gx@bombadil.infradead.org> (raw)
In-Reply-To: <202110051354.294E28AC87@keescook>
On Tue, Oct 05, 2021 at 01:55:35PM -0700, Kees Cook wrote:
> On Mon, Sep 27, 2021 at 09:38:04AM -0700, Luis Chamberlain wrote:
> > Provide a simple state machine to fix races with driver exit where we
> > remove the CPU multistate callbacks and re-initialization / creation of
> > new per CPU instances which should be managed by these callbacks.
> >
> > The zram driver makes use of cpu hotplug multistate support, whereby it
> > associates a struct zcomp per CPU. Each struct zcomp represents a
> > compression algorithm in charge of managing compression streams per
> > CPU. Although a compiled zram driver only supports a fixed set of
> > compression algorithms, each zram device gets a struct zcomp allocated
> > per CPU. The "multi" in CPU hotplug multstate refers to these per
> > cpu struct zcomp instances. Each of these will have the CPU hotplug
> > callback called for it on CPU plug / unplug. The kernel's CPU hotplug
> > multistate keeps a linked list of these different structures so that
> > it will iterate over them on CPU transitions.
> >
> > By default at driver initialization we will create just one zram device
> > (num_devices=1) and a zcomp structure then set for the now default
> > lzo-rle comrpession algorithm. At driver removal we first remove each
> > zram device, and so we destroy the associated struct zcomp per CPU. But
> > since we expose sysfs attributes to create new devices or reset /
> > initialize existing zram devices, we can easily end up re-initializing
> > a struct zcomp for a zram device before the exit routine of the module
> > removes the cpu hotplug callback. When this happens the kernel's CPU
> > hotplug will detect that at least one instance (struct zcomp for us)
> > exists. This can happen in the following situation:
> >
> > CPU 1 CPU 2
> >
> > disksize_store(...);
> > class_unregister(...);
> > idr_for_each(...);
> > zram_debugfs_destroy();
> >
> > idr_destroy(...);
> > unregister_blkdev(...);
> > cpuhp_remove_multi_state(...);
>
> So this is strictly separate from the sysfs/module unloading race?
It is only related in the sense that the sysfs/module unloading race
happened *after* this other issue, but addressing these through
separate threads created a break in conversation and focus. For
instance, a theoretical race was mentioned in one thread, which
I worked to prove/disprove and then I disproved it was not possible.
But at this point, yes, this is a purely separate issue, and this
patch *should* be picked up already.
Andrew, can you merge this? It already has the respective maintainer
Ack, and I can continue to work on the rest of the patches. The only
issue I can think of would be a conflict with the last patch but
that's a oneliner, I think chances are low that would create a conflict
if its all merged separately, and if so, it should be an easy fix for
a merge conflict.
Luis
next prev parent reply other threads:[~2021-10-11 18:27 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 [this message]
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
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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