From: Nicolai Stange <nstange@suse.de>
To: Bart Van Assche <bvanassche@acm.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>,
axboe@kernel.dk, viro@zeniv.linux.org.uk,
gregkh@linuxfoundation.org, rostedt@goodmis.org,
mingo@redhat.com, jack@suse.cz, ming.lei@redhat.com,
nstange@suse.de, mhocko@suse.com, linux-block@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
Omar Sandoval <osandov@fb.com>, Hannes Reinecke <hare@suse.com>,
Michal Hocko <mhocko@kernel.org>
Subject: Re: [RFC 3/3] block: avoid deferral of blk_release_queue() work
Date: Thu, 02 Apr 2020 16:49:37 +0200 [thread overview]
Message-ID: <87o8saj62m.fsf@suse.de> (raw)
In-Reply-To: <774a33e8-43ba-143f-f6fd-9cb0ae0862ac@acm.org> (Bart Van Assche's message of "Wed, 1 Apr 2020 20:39:48 -0700")
Bart Van Assche <bvanassche@acm.org> writes:
> On 2020-04-01 17:00, Luis Chamberlain wrote:
>> Commit dc9edc44de6c ("block: Fix a blk_exit_rl() regression") moved
>> the blk_release_queue() into a workqueue after a splat floated around
>> with some work here which could sleep in blk_exit_rl().
>>
>> On recent commit db6d9952356 ("block: remove request_list code") though
>> Jens Axboe removed this code, now merged since v5.0. We no longer have
>> to defer this work.
>>
>> By doing this we also avoid failing to detach / attach a block
>> device with a BLKTRACESETUP. This issue can be reproduced with
>> break-blktrace [0] using:
>>
>> break-blktrace -c 10 -d -s
>>
>> The kernel does not crash without this commit, it just fails to
>> create the block device because the prior block device removal
>> deferred work is pending. After this commit we can use the above
>> flaky use of blktrace without an issue.
>>
>> [0] https://github.com/mcgrof/break-blktrace
>>
>> Cc: Bart Van Assche <bvanassche@acm.org>
>> Cc: Omar Sandoval <osandov@fb.com>
>> Cc: Hannes Reinecke <hare@suse.com>
>> Cc: Nicolai Stange <nstange@suse.de>
>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> Cc: Michal Hocko <mhocko@kernel.org>
>> Suggested-by: Nicolai Stange <nstange@suse.de>
>> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
>> ---
>> block/blk-sysfs.c | 18 +++++-------------
>> 1 file changed, 5 insertions(+), 13 deletions(-)
>>
>> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
>> index 20f20b0fa0b9..f159b40899ee 100644
>> --- a/block/blk-sysfs.c
>> +++ b/block/blk-sysfs.c
>> @@ -862,8 +862,8 @@ static void blk_exit_queue(struct request_queue *q)
>>
>>
>> /**
>> - * __blk_release_queue - release a request queue
>> - * @work: pointer to the release_work member of the request queue to be released
>> + * blk_release_queue - release a request queue
>> + * @kojb: pointer to the kobj representing the request queue
>> *
>> * Description:
>> * This function is called when a block device is being unregistered. The
>> @@ -873,9 +873,10 @@ static void blk_exit_queue(struct request_queue *q)
>> * of the request queue reaches zero, blk_release_queue is called to release
>> * all allocated resources of the request queue.
>> */
>> -static void __blk_release_queue(struct work_struct *work)
>> +static void blk_release_queue(struct kobject *kobj)
>> {
>> - struct request_queue *q = container_of(work, typeof(*q), release_work);
>> + struct request_queue *q =
>> + container_of(kobj, struct request_queue, kobj);
>>
>> if (test_bit(QUEUE_FLAG_POLL_STATS, &q->queue_flags))
>> blk_stat_remove_callback(q, q->poll_cb);
>> @@ -905,15 +906,6 @@ static void __blk_release_queue(struct work_struct *work)
>> call_rcu(&q->rcu_head, blk_free_queue_rcu);
>> }
>>
>> -static void blk_release_queue(struct kobject *kobj)
>> -{
>> - struct request_queue *q =
>> - container_of(kobj, struct request_queue, kobj);
>> -
>> - INIT_WORK(&q->release_work, __blk_release_queue);
>> - schedule_work(&q->release_work);
>> -}
>> -
>> static const struct sysfs_ops queue_sysfs_ops = {
>> .show = queue_attr_show,
>> .store = queue_attr_store,
>
> The description of this patch mentions a single blk_release_queue() call
> that happened in the past from a context from which sleeping is not
> allowed and from which sleeping is allowed today. Have all other
> blk_release_queue() / blk_put_queue() calls been verified to see whether
> none of these happens from a context from which sleeping is not allowed?
I've just done this today and found the following potentially
problematic call paths to blk_put_queue().
1.) mem_cgroup_throttle_swaprate() takes a spinlock and
calls blkcg_schedule_throttle()->blk_put_queue().
Also note that AFAICS mem_cgroup_try_charge_delay() can be called
with GFP_ATOMIC.
2.) scsi_unblock_requests() gets called from a lot of drivers and
invoke blk_put_queue() through
scsi_unblock_requests() -> scsi_run_host_queues() ->
scsi_starved_list_run() -> blk_put_queue().
Most call sites are fine, the ones which are not are:
a.) pmcraid_complete_ioa_reset(). This gets assigned
to struct pmcraid_cmd's ->cmd_done and later invoked
under a spinlock.
b.) qla82xx_fw_dump() and qla8044_fw_dump().
These can potentially block w/o this patch already,
because both invoke qla2x00_wait_for_chip_reset().
However, they can get called from IRQ context. For example,
qla82xx_intr_handler(), qla82xx_msix_default() and
qla82xx_poll() call qla2x00_async_event(), which calls
->fw_dump().
The aforementioned functions can also reach ->fw_dump() through
qla24xx_process_response_queue()->qlt_handle_abts_recv()->qlt_response_pkt_all_vps()
->qlt_response_pkt()->qlt_handle_abts_completion()->qlt_chk_unresolv_exchg()
-> ->fw_dump().
But I'd consider this a problem with the driver -- either
->fw_dump() can sleep and must not be called from IRQ context
or they must not invoke qla2x00_wait_for_hba_ready().
(I can share the full analysis, but it's lengthy and contains nothing
interesting except for what is listed above).
One final note though: If I'm not mistaken, then the final
blk_put_queue() can in principle block even today, simply by virtue of
the kernfs operations invoked through
kobject_put()->kobject_release()->kobject_cleanup()->kobject_del()
->sysfs_remove_dir()->kernfs_remove()->mutex_lock()?
Thanks,
Nicolai
--
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg), GF: Felix Imendörffer
next prev parent reply other threads:[~2020-04-02 14:49 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-01 23:59 [RFC 0/3] block: address blktrace use-after-free Luis Chamberlain
2020-04-02 0:00 ` [RFC 1/3] block: move main block debugfs initialization to its own file Luis Chamberlain
2020-04-05 3:12 ` Bart Van Assche
2020-04-06 14:23 ` Luis Chamberlain
2020-04-02 0:00 ` [RFC 2/3] blktrace: fix debugfs use after free Luis Chamberlain
2020-04-02 1:57 ` Eric Sandeen
2020-04-02 16:14 ` Luis Chamberlain
2020-04-05 3:39 ` Bart Van Assche
2020-04-06 1:27 ` Eric Sandeen
2020-04-06 4:25 ` Bart Van Assche
2020-04-06 9:18 ` Nicolai Stange
2020-04-06 15:19 ` Luis Chamberlain
2020-04-07 8:15 ` Luis Chamberlain
2020-04-06 14:29 ` Eric Sandeen
2020-04-07 8:09 ` Luis Chamberlain
2020-04-06 15:14 ` Luis Chamberlain
2020-04-02 0:00 ` [RFC 3/3] block: avoid deferral of blk_release_queue() work Luis Chamberlain
2020-04-02 3:39 ` Bart Van Assche
2020-04-02 14:49 ` Nicolai Stange [this message]
2020-04-06 9:11 ` Nicolai Stange
2020-04-09 18:11 ` Luis Chamberlain
2020-04-02 7:44 ` [RFC 0/3] block: address blktrace use-after-free Greg KH
2020-04-03 8:19 ` Ming Lei
2020-04-03 14:06 ` Luis Chamberlain
2020-04-03 14:13 ` Bart Van Assche
2020-04-03 19:49 ` Luis Chamberlain
2020-04-07 2:47 ` yukuai (C)
2020-04-07 19:00 ` Luis Chamberlain
2020-04-09 20:59 ` Luis Chamberlain
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