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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: Mon, 10 Aug 2020 14:03:17 +0200
Message-ID: <60150284-be13-d373-5448-651b72a7c4c9@puri.sm> (raw)
In-Reply-To: <20200809152643.GA277165@rowland.harvard.edu>

On 09.08.20 17:26, Alan Stern wrote:
> On Sun, Aug 09, 2020 at 11:20:22AM +0200, Martin Kepplinger wrote:
>> Hey Alan, I'm really glad for that, I suspected some of this but I have
>> little experience in scsi/block layers, so that is super helpful.
>>
>> I'd appreciate an opinion on the below workaround that *seems* to work
>> now (let's see, I had thought so before :)
>>
>> Whether or not this helps to find a real solution, let's see. But
>> integration of such a flag in the error handling paths is what's
>> interesting for now:
>>
>>
>> --- a/drivers/scsi/scsi_error.c
>> +++ b/drivers/scsi/scsi_error.c
>> @@ -565,6 +565,17 @@ 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 expecting_media_change in
>> +				 * scsi_noretry_cmd() because we need
>> +				 * to override possible "failfast" overrides
>> +				 * that block readahead can cause.
>> +				 */
>> +				return NEEDS_RETRY;
> 
> 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 {
 		/*
 		 * no more retries - report this one back to upper level.
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index d90fefffe31b..bb583e403b81 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -3642,6 +3642,8 @@ static int sd_resume(struct device *dev)
 	if (!sdkp)	/* E.g.: runtime resume at the start of sd_probe() */
 		return 0;

+	sdkp->device->expecting_media_change = 1;
+
 	if (!sdkp->device->manage_start_stop)
 		return 0;

diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index bc5909033d13..f5fc1af68e00 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -169,6 +169,7 @@ struct scsi_device {
 				 * this device */
 	unsigned expecting_cc_ua:1; /* Expecting a CHECK_CONDITION/UNIT_ATTN
 				     * because we did a bus reset. */
+	unsigned expecting_media_change:1;
 	unsigned use_10_for_rw:1; /* first try 10-byte read / write */
 	unsigned use_10_for_ms:1; /* first try 10-byte mode sense/select */
 	unsigned set_dbd_for_ms:1; /* Set "DBD" field in mode sense */
-- 

  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 [this message]
2020-08-10 14:13                                                                     ` Alan Stern
2020-08-11  7:55                                                                       ` Martin Kepplinger
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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