From: John Garry <john.g.garry@oracle.com>
To: Bart Van Assche <bvanassche@acm.org>,
martin.petersen@oracle.com,
james.bottomley@hansenpartnership.com
Cc: linux-scsi@vger.kernel.org, jiangjianjun3@huawei.com
Subject: Re: [PATCH 2/6] scsi: scsi_debug: Stop using READ/WRITE_ONCE() when accessing sdebug_defer.defer_t
Date: Fri, 14 Nov 2025 09:02:05 +0000 [thread overview]
Message-ID: <a0e4fdd2-3dce-46c8-94ad-cdddbf90676a@oracle.com> (raw)
In-Reply-To: <0108b7fd-77c5-4aa5-a761-2a7640d2a024@acm.org>
On 13/11/2025 17:45, Bart Van Assche wrote:
>
> On 11/13/25 5:36 AM, John Garry wrote:
>> Using READ/WRITE_ONCE() means that the read or write is not torn by the
>> compiler.
>>
>> READ/WRITE_ONCE() is always used when accessing sdebug_defer.defer_t.
>>
>> However, we also guard the access in a spinlock when accessing that
>> member,
>> and spinlock already guarantees no tearing, so stop using
>> READ/WRITE_ONCE().
>
> According to the Linux kernel memory model, if a variable is accessed
> outside a critical section then READ_ONCE() and WRITE_ONCE() must be
> used when accessing that variable inside a critical section.
So do you see a problem with this patch? As mentioned,
sdebug_defer.defer_t is already only accessed with a spinlock held
(sdebug_scsi_cmd.lock) (which I consider being a critical section).
Thanks,
John
next prev parent reply other threads:[~2025-11-14 9:02 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-13 13:36 [PATCH RFT 0/6] scsi_debug: fake timeout handling improvements John Garry
2025-11-13 13:36 ` [PATCH 1/6] scsi: scsi_debug: Stop printing extra function name in debug logs John Garry
2025-11-13 13:36 ` [PATCH 2/6] scsi: scsi_debug: Stop using READ/WRITE_ONCE() when accessing sdebug_defer.defer_t John Garry
2025-11-13 17:45 ` Bart Van Assche
2025-11-14 9:02 ` John Garry [this message]
2025-11-14 16:27 ` Bart Van Assche
2025-11-13 13:36 ` [PATCH 3/6] scsi: scsi_debug: Drop NULL scsi_cmnd check in sdebug_q_cmd_complete() John Garry
2025-11-13 17:46 ` Bart Van Assche
2025-11-14 9:02 ` John Garry
2025-11-13 13:36 ` [PATCH RFT 4/6] scsi: scsi_debug: Call sdebug_q_cmd_complete() from sdebug_blk_mq_poll_iter() John Garry
2025-11-13 13:36 ` [PATCH RFT 5/6] scsi: scsi_debug: Clear sd_dp->defer_t in sdebug_q_cmd_complete() John Garry
2025-11-13 13:36 ` [PATCH RFT 6/6] scsi: scsi_debug: Add special abort handling for fake timeout John Garry
2025-12-01 15:32 ` [PATCH RFT 0/6] scsi_debug: fake timeout handling improvements John Garry
2025-12-17 2:48 ` Martin K. Petersen
2025-12-17 12:48 ` John Garry
2026-04-16 2:30 ` JiangJianJun
2026-04-16 9:12 ` John Garry
2026-01-04 21:43 ` (subset) " Martin K. Petersen
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