From: Minchan Kim <minchan@kernel.org>
To: Luis Chamberlain <mcgrof@kernel.org>
Cc: ngupta@vflare.org, sergey.senozhatsky.work@gmail.com,
axboe@kernel.dk, mbenes@suse.com, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] zram: fix crashes due to use of cpu hotplug multistate
Date: Mon, 8 Mar 2021 18:55:30 -0800 [thread overview]
Message-ID: <YEbjom8FIclEgRYv@google.com> (raw)
In-Reply-To: <20210306022035.11266-2-mcgrof@kernel.org>
On Sat, Mar 06, 2021 at 02:20:34AM +0000, Luis Chamberlain wrote:
> The zram driver makes use of cpu hotplug multistate support,
> whereby it associates a zram compression stream per CPU. To
> support CPU hotplug multistate a callback enabled to allow
> the driver to do what it needs when a CPU hotplugs.
>
> It is however currently possible to end up removing the
> zram driver callback prior to removing the zram compression
> streams per CPU. This would leave these compression streams
> hanging.
>
> We need to fix ordering for driver load / removal, zram
> device additions, in light of the driver's use of cpu
> hotplug multistate. Since the zram driver exposes many
> sysfs attribute which can also muck with the comrpession
> streams this also means we can hit page faults today easily.
Hi Luis,
First of all, thanks for reporting the ancient bugs.
Looks like you found several bugs and I am trying to digest them
from your description to understand more clear. I need to ask
stupid questions, first.
If I understand correctly, bugs you found were related to module
unloading race while the zram are still working.
If so, couldn't we fix the bug like this(it's not a perfect
patch but just wanted to show close module unloading race)?
(I might miss other pieces here. Let me know. Thanks!)
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index a711a2e2a794..646ae9e0b710 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1696,6 +1696,8 @@ static void zram_reset_device(struct zram *zram)
return;
}
+ module_put(THIS_MODULE);
+
comp = zram->comp;
disksize = zram->disksize;
zram->disksize = 0;
@@ -1744,13 +1746,19 @@ static ssize_t disksize_store(struct device *dev,
goto out_free_meta;
}
+ if (!try_module_get(THIS_MODULE))
+ goto out_free_zcomp;
+
zram->comp = comp;
zram->disksize = disksize;
+
set_capacity_and_notify(zram->disk, zram->disksize >> SECTOR_SHIFT);
up_write(&zram->init_lock);
return len;
+out_free_zcomp:
+ zcomp_destroy(comp);
out_free_meta:
zram_meta_free(zram, disksize);
out_unlock:
next prev parent reply other threads:[~2021-03-09 2:56 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-06 2:20 [PATCH 0/2] zram: fix few ltp zram02.sh crashes Luis Chamberlain
2021-03-06 2:20 ` [PATCH 1/2] zram: fix crashes due to use of cpu hotplug multistate Luis Chamberlain
2021-03-09 2:55 ` Minchan Kim [this message]
2021-03-10 13:11 ` Luis Chamberlain
2021-03-10 21:25 ` Luis Chamberlain
2021-03-12 2:08 ` Minchan Kim
2021-03-10 21:21 ` Luis Chamberlain
2021-03-12 2:14 ` Minchan Kim
2021-03-12 18:32 ` Luis Chamberlain
2021-03-12 19:28 ` Minchan Kim
2021-03-19 19:09 ` Luis Chamberlain
2021-03-22 16:37 ` Minchan Kim
2021-03-22 20:41 ` Luis Chamberlain
2021-03-22 22:12 ` Minchan Kim
2021-04-01 23:59 ` Luis Chamberlain
2021-04-02 7:54 ` Greg KH
2021-04-02 18:30 ` Luis Chamberlain
2021-04-03 6:13 ` Greg KH
[not found] ` <20210406003152.GZ4332@42.do-not-panic.com>
2021-04-06 12:00 ` Miroslav Benes
2021-04-06 15:54 ` Josh Poimboeuf
2021-04-07 14:09 ` Peter Zijlstra
2021-04-07 15:30 ` Josh Poimboeuf
2021-04-07 16:48 ` Peter Zijlstra
2021-04-07 20:17 ` Josh Poimboeuf
2021-04-08 6:18 ` Greg KH
2021-04-08 13:16 ` Steven Rostedt
2021-04-08 13:37 ` Josh Poimboeuf
2021-04-08 1:37 ` Thomas Gleixner
2021-04-08 6:16 ` Greg KH
2021-04-08 8:01 ` Jiri Kosina
2021-04-08 8:09 ` Greg KH
2021-04-08 8:35 ` Jiri Kosina
2021-04-08 8:55 ` Greg KH
2021-04-08 18:40 ` Luis Chamberlain
2021-04-09 3:01 ` Kees Cook
2021-04-05 17:07 ` Minchan Kim
2021-04-05 19:00 ` Luis Chamberlain
2021-04-05 19:58 ` Minchan Kim
2021-04-06 0:29 ` Luis Chamberlain
2021-04-07 1:23 ` Minchan Kim
2021-04-07 1:38 ` Minchan Kim
2021-04-07 14:52 ` Luis Chamberlain
2021-04-07 14:50 ` Luis Chamberlain
2021-03-06 2:20 ` [PATCH 2/2] zram: fix races of sysfs attribute removal and usage Luis Chamberlain
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