From: Martin Kepplinger <martin.kepplinger@puri.sm>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: James Bottomley <James.Bottomley@hansenpartnership.com>,
Bart Van Assche <bvanassche@acm.org>,
Can Guo <cang@codeaurora.org>,
martin.petersen@oracle.com, linux-scsi@vger.kernel.org,
linux-kernel@vger.kernel.org, kernel@puri.sm
Subject: Re: [PATCH] scsi: sd: add runtime pm to open / release
Date: Tue, 11 Aug 2020 09:55:54 +0200 [thread overview]
Message-ID: <6f0c530f-4309-ab1e-393b-83bf8367f59e@puri.sm> (raw)
In-Reply-To: <20200810141343.GA299045@rowland.harvard.edu>
On 10.08.20 16:13, Alan Stern wrote:
> On Mon, Aug 10, 2020 at 02:03:17PM +0200, Martin Kepplinger wrote:
>> On 09.08.20 17:26, Alan Stern wrote:
>>> This is a somewhat fragile approach. You don't know for certain that
>>> scsi_noretry_cmd will be called. Also, scsi_noretry_cmd can be called
>>> from other places.
>>>
>>> It would be better to clear the expecting_media_change flag just before
>>> returning from scsi_decide_disposition. That way its use is localized
>>> to one routine, not spread out between two.
>>>
>>> Alan Stern
>>>
>>
>> Hi Alan,
>>
>> maybe you're right. I initially just thought that I'd allow for specific
>> error codes in scsi_noretry_cmd() to return non-NULL (BUS_BUSY, PARITY,
>> ERROR) despite having the flag set.
>>
>> The below version works equally fine for me but I'm not sure if it's
>> actually more safe.
>>
>> James, when exposing a new writable sysfs option like
>> "suspend_no_media_change"(?) that drivers can check before setting the
>> new "expecting_media_change" flag (during resume), would this addition
>> make sense to you?
>>
>> thanks,
>>
>> martin
>>
>>
>>
>> --- a/drivers/scsi/scsi_error.c
>> +++ b/drivers/scsi/scsi_error.c
>> @@ -565,6 +565,18 @@ int scsi_check_sense(struct scsi_cmnd *scmd)
>> return NEEDS_RETRY;
>> }
>> }
>> + if (scmd->device->expecting_media_change) {
>> + if (sshdr.asc == 0x28 && sshdr.ascq == 0x00) {
>> + /*
>> + * clear the expecting_media_change in
>> + * scsi_decide_disposition() because we
>> + * need to catch possible "fail fast" overrides
>> + * that block readahead can cause.
>> + */
>> + return NEEDS_RETRY;
>> + }
>> + }
>> +
>> /*
>> * we might also expect a cc/ua if another LUN on the target
>> * reported a UA with an ASC/ASCQ of 3F 0E -
>> @@ -1944,9 +1956,19 @@ int scsi_decide_disposition(struct scsi_cmnd *scmd)
>> * the request was not marked fast fail. Note that above,
>> * even if the request is marked fast fail, we still requeue
>> * for queue congestion conditions (QUEUE_FULL or BUSY) */
>> - if ((++scmd->retries) <= scmd->allowed
>> - && !scsi_noretry_cmd(scmd)) {
>> - return NEEDS_RETRY;
>> + if ((++scmd->retries) <= scmd->allowed) {
>> + /*
>> + * but scsi_noretry_cmd() cannot override the
>> + * expecting_media_change flag.
>> + */
>> + if (!scsi_noretry_cmd(scmd) ||
>> + scmd->device->expecting_media_change) {
>> + scmd->device->expecting_media_change = 0;
>> + return NEEDS_RETRY;
>> + } else {
>> + /* marked fast fail and not expected. */
>> + return SUCCESS;
>> + }
>> } else {
>
> This may not matter... but it's worth pointing out that
> expecting_media_change doesn't get cleared if ++scmd->retries >
> scmd->allowed.
absolutely worth pointing out and I'm not yet sure about that one.
>
> It also doesn't get cleared in cases where the device _doesn't_
> report a Unit Attention.
true. but don't we set the flag for a future UA we don't yet know of? If
we would want to clear it outside of a UA, I think we'd need to keep
track of a suspend/resume cycle and if we see that we *had* successfully
"done requests" after resuming, we could clear it...
>
> Alan Stern
>
next prev parent reply other threads:[~2020-08-11 7:56 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-23 11:10 [PATCH] scsi: sd: add runtime pm to open / release Martin Kepplinger
2020-06-24 13:33 ` Bart Van Assche
2020-06-25 8:16 ` Martin Kepplinger
2020-06-25 14:52 ` Alan Stern
2020-06-26 3:53 ` Bart Van Assche
2020-06-26 15:07 ` Bart Van Assche
2020-06-26 15:44 ` Alan Stern
2020-06-28 2:37 ` Bart Van Assche
2020-06-28 13:10 ` Alan Stern
2020-06-29 9:42 ` Martin Kepplinger
2020-06-29 16:15 ` Alan Stern
2020-06-29 16:56 ` Bart Van Assche
2020-06-29 17:40 ` Alan Stern
2020-06-30 3:33 ` Martin Kepplinger
2020-06-30 13:38 ` Alan Stern
2020-06-30 15:59 ` Bart Van Assche
2020-06-30 18:02 ` Alan Stern
2020-06-30 19:23 ` Bart Van Assche
2020-06-30 19:38 ` Alan Stern
2020-06-30 23:31 ` Bart Van Assche
2020-07-01 0:49 ` Alan Stern
2020-07-06 16:41 ` Alan Stern
2020-07-28 7:02 ` Martin Kepplinger
2020-07-28 20:02 ` Alan Stern
2020-07-29 14:12 ` Martin Kepplinger
2020-07-29 14:32 ` Alan Stern
2020-07-29 14:44 ` Martin K. Petersen
2020-07-29 14:56 ` Alan Stern
2020-07-29 14:46 ` James Bottomley
2020-07-29 14:53 ` James Bottomley
2020-07-29 15:40 ` Martin Kepplinger
2020-07-29 15:44 ` James Bottomley
2020-07-29 16:43 ` Martin Kepplinger
2020-07-29 18:25 ` Alan Stern
2020-07-29 18:29 ` James Bottomley
2020-07-30 8:52 ` Martin Kepplinger
2020-07-30 8:54 ` Martin Kepplinger
2020-07-30 15:10 ` Alan Stern
2020-08-04 9:39 ` Martin Kepplinger
2020-08-07 9:51 ` Martin Kepplinger
2020-08-07 14:30 ` Alan Stern
2020-08-08 6:59 ` Martin Kepplinger
2020-08-08 15:05 ` Alan Stern
2020-08-09 9:20 ` Martin Kepplinger
2020-08-09 15:26 ` Alan Stern
2020-08-10 12:03 ` Martin Kepplinger
2020-08-10 14:13 ` Alan Stern
2020-08-11 7:55 ` Martin Kepplinger [this message]
2020-08-11 13:48 ` Alan Stern
2020-08-23 14:57 ` [PATCH] block: Fix bug in runtime-resume handling Alan Stern
2020-08-24 17:48 ` Bart Van Assche
2020-08-24 20:13 ` Alan Stern
2020-08-26 7:48 ` Martin Kepplinger
2020-08-27 17:42 ` Martin Kepplinger
2020-08-27 20:29 ` Alan Stern
2020-08-29 7:24 ` Martin Kepplinger
2020-08-29 15:26 ` Alan Stern
2020-08-29 16:33 ` Martin Kepplinger
2020-08-29 18:56 ` Alan Stern
2020-08-30 0:38 ` Bart Van Assche
2020-08-30 1:06 ` Alan Stern
2020-07-29 15:40 ` [PATCH] scsi: sd: add runtime pm to open / release Alan Stern
2020-07-29 15:49 ` James Bottomley
2020-07-29 16:17 ` Alan Stern
2020-07-29 15:52 ` Martin Kepplinger
2020-07-29 18:10 ` Douglas Gilbert
2020-07-30 8:05 ` Martin Kepplinger
2020-07-30 15:14 ` Alan Stern
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