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From: Chris Mason <clm@fb.com>
To: "Theodore Y. Ts'o" <tytso@mit.edu>
Cc: Linux Filesystem Development List <linux-fsdevel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH -v2] memcg: fix a crash in wb_workfn when a device disappears
Date: Fri, 3 Jan 2020 17:46:29 +0000
Message-ID: <527DCBC3-28D2-4BFE-A99C-8ED65A613A20@fb.com> (raw)
In-Reply-To: <20200103171517.GA4253@mit.edu>

On 3 Jan 2020, at 12:15, Theodore Y. Ts'o wrote:

> On Fri, Dec 27, 2019 at 07:52:11PM -0500, Theodore Ts'o wrote:
>>
>> Fortunately, it looks like the rest of the writeback path is 
>> perfectly
>> happy with bdi->dev and bdi->owner being NULL, so the simplest fix is
>> to create a bdi_dev_name() function which can handle bdi->dev being
>> NULL.  This also allows us to bulletproof the writeback tracepoints 
>> to
>> prevent them from dereferencing a NULL pointer and crashing the 
>> kernel
>> if one is tracing with memcg's enabled, and an iSCSI device dies or a
>> USB storage stick is pulled.
>>
>> Previous-Version-Link: 
>> https://lore.kernel.org/r/20191227194829.150110-1-tytso@mit.edu
>> Google-Bug-Id: 145475544
>> Tested: fs smoke test
>> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
>> ---
>>
>> Notes:
>>     v2: add #include for linux/device.h
>>
>>  fs/fs-writeback.c                |  2 +-
>>  include/linux/backing-dev.h      | 10 +++++++++
>>  include/trace/events/writeback.h | 37 
>> +++++++++++++++-----------------
>>  mm/backing-dev.c                 |  1 +
>>  4 files changed, 29 insertions(+), 21 deletions(-)
>
> Ping?
>
> Any comments?  Any objections if I carry this patch[1] in the ext4
> tree?  Or would it be better for Andrew to carry it in the linux-mm
> tree?
>
> [1] https://lore.kernel.org/k/20191227203117.152399-1-tytso@mit.edu

Seems sane to me, and we probably want this even if del_gendisk() 
embraces the brave new memcg world because synchronizing all of this is 
going to get messy.

-chris

  reply index

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-27 19:48 [PATCH] " Theodore Ts'o
2019-12-27 20:31 ` Theodore Ts'o
2019-12-27 21:16 ` kbuild test robot
2019-12-27 21:19   ` Theodore Y. Ts'o
2019-12-27 22:32 ` kbuild test robot
2019-12-28  0:52 ` [PATCH -v2] " Theodore Ts'o
2020-01-03 17:15   ` Theodore Y. Ts'o
2020-01-03 17:46     ` Chris Mason [this message]
2020-01-07 23:33   ` Andrew Morton
2020-01-08  2:12     ` Theodore Y. Ts'o

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