From: Bart Van Assche <bvanassche@acm.org>
To: Martin Wilck <mwilck@suse.com>,
Mike Christie <michael.christie@oracle.com>,
Christoph Hellwig <hch@lst.de>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>,
Ming Lei <ming.lei@redhat.com>,
Bart Van Assche <Bart.VanAssche@sandisk.com>,
James Bottomley <jejb@linux.vnet.ibm.com>,
linux-scsi@vger.kernel.org, linux-block@vger.kernel.org,
Hannes Reinecke <hare@suse.de>
Subject: Re: [PATCH v3 4/8] scsi: call scsi_stop_queue() without state_mutex held
Date: Mon, 12 Jun 2023 06:41:12 -0700 [thread overview]
Message-ID: <dd9acaed-89de-6402-a763-7db6736a6f5f@acm.org> (raw)
In-Reply-To: <2bfdb9a65668109c204f7d4677bd717f049b1e83.camel@suse.com>
On 6/12/23 04:15, Martin Wilck wrote:
> I guess the race that Bart was hinting at is hard to trigger.
Are you sure about this? I think this scenario can be triggered by
writing into the sysfs attribute that changes the SCSI device state
while a scsi_target_block() call is in progress. See also
store_state_field().
> I would like to remark that the fact that we need to hold the SCSI
> state_mutex while calling blk_mq_quiesce_queue_nowait() looks like a
> layering issue to me. Not sure if, and how, this could be avoided,
> though.
I do not agree that this is a layering issue. Is holding a mutex around
a call of a function in a lower layer ever a layering issue?
What matters is to be very careful with locks while invoking callback
functions. See also slide 7 in Ousterhout's presentation "Why Threads
Are A Bad Idea (for most purposes)" from 1996
(https://web.stanford.edu/~ouster/cgi-bin/papers/threads.pdf).
Bart.
next prev parent reply other threads:[~2023-06-12 13:41 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-07 18:22 [PATCH v3 0/8] scsi: fixes for targets with many LUNs, and scsi_target_block rework mwilck
2023-06-07 18:22 ` [PATCH v3 1/8] bsg: increase number of devices mwilck
2023-06-07 18:22 ` [PATCH v3 2/8] scsi: sg: " mwilck
2023-06-07 18:22 ` [PATCH v3 3/8] scsi: merge scsi_internal_device_block() and device_block() mwilck
2023-06-07 19:10 ` Bart Van Assche
2023-06-08 5:42 ` Christoph Hellwig
2023-06-07 18:22 ` [PATCH v3 4/8] scsi: call scsi_stop_queue() without state_mutex held mwilck
2023-06-07 19:16 ` Bart Van Assche
2023-06-07 19:37 ` Martin Wilck
2023-06-07 20:07 ` Martin Wilck
2023-06-08 5:44 ` Christoph Hellwig
2023-06-08 14:12 ` Bart Van Assche
2023-06-08 18:54 ` Mike Christie
2023-06-12 11:15 ` Martin Wilck
2023-06-12 13:41 ` Bart Van Assche [this message]
2023-06-07 18:22 ` [PATCH v3 5/8] scsi: don't wait for quiesce in scsi_stop_queue() mwilck
2023-06-08 5:46 ` Christoph Hellwig
2023-06-07 18:22 ` [PATCH v3 6/8] scsi: don't wait for quiesce in scsi_device_block() mwilck
2023-06-07 18:22 ` [PATCH v3 7/8] scsi: have scsi_target_block() expect a scsi_target parent argument mwilck
2023-06-08 5:48 ` Christoph Hellwig
2023-06-07 18:22 ` [PATCH v3 8/8] scsi: add Scsi_Host argument to scsi_target_block() mwilck
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