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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
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
> 

  reply index

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-23 11:10 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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