Re: [PATCH V2] scsi: save/restore command resid for error handling

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On 2019/09/30 17:42, Finn Thain wrote:
> On Sat, 28 Sep 2019, Damien Le Moal wrote:
> 
>> When a non-passthrough command is terminated with CHECK CONDITION,
>> request sense is executed by hijacking the command descriptor. Since
>> scsi_eh_prep_cmnd() and scsi_eh_restore_cmnd() do not save/restore the
>> original command resid, the value returned on failure of the original
>> command is lost and replaced with the value set by the execution of the
>> request sense command. This value may in many instances be unaligned to
>> the device sector size, causing sd_done() to print a warning message
>> about the incorrect unaligned resid before the command is retried or
>> aborted.
>>
>> Fix this problem by saving the original command resid in struct
>> scsi_eh_save using scsi_eh_prep_cmnd() and restoring it in
>> scsi_eh_restore_cmnd(). In addition, to make sure that the request sense
>> command is executed with a correctly initialized command structure, also
>> reset resid to 0 in scsi_eh_prep_cmnd() after saving the original
>> command resid value in struct scsi_eh_save.
>>
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
>> ---
>>
>> Changes from V1:
>> * Dropped patch 2
>> * Add resid reset in scsi_eh_prep_cmnd()
>>
>>  drivers/scsi/scsi_error.c | 3 +++
>>  include/scsi/scsi_eh.h    | 1 +
>>  2 files changed, 4 insertions(+)
>>
>> diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
>> index 1c470e31ae81..f53828bf7ad7 100644
>> --- a/drivers/scsi/scsi_error.c
>> +++ b/drivers/scsi/scsi_error.c
>> @@ -967,6 +967,7 @@ void scsi_eh_prep_cmnd(struct scsi_cmnd *scmd, struct scsi_eh_save *ses,
>>  	ses->data_direction = scmd->sc_data_direction;
>>  	ses->sdb = scmd->sdb;
>>  	ses->result = scmd->result;
>> +	ses->resid = scsi_get_resid(scmd);
>>  	ses->underflow = scmd->underflow;
>>  	ses->prot_op = scmd->prot_op;
>>  	ses->eh_eflags = scmd->eh_eflags;
>> @@ -977,6 +978,7 @@ void scsi_eh_prep_cmnd(struct scsi_cmnd *scmd, struct scsi_eh_save *ses,
>>  	memset(scmd->cmnd, 0, BLK_MAX_CDB);
>>  	memset(&scmd->sdb, 0, sizeof(scmd->sdb));
>>  	scmd->result = 0;
>> +	scsi_set_resid(scmd, 0);
>>  
>>  	if (sense_bytes) {
>>  		scmd->sdb.length = min_t(unsigned, SCSI_SENSE_BUFFERSIZE,
>> @@ -1029,6 +1031,7 @@ void scsi_eh_restore_cmnd(struct scsi_cmnd* scmd, struct scsi_eh_save *ses)
>>  	scmd->sc_data_direction = ses->data_direction;
>>  	scmd->sdb = ses->sdb;
>>  	scmd->result = ses->result;
>> +	scsi_set_resid(scmd, ses->resid);
> 
> When saving and restoring state, perhaps it makes more sense to bypass the 
> higher level getter/setter API? Open-coded assignment statements are 
> already prevalent here, rather than calls to e.g. scsi_set_prot_op(), 
> set_msg_byte() etc. (There may be no code elsewhere that could tell the 
> difference, but we can't use "private" members to prove it, unlike C++.)
> 
>>  	scmd->underflow = ses->underflow;
>>  	scmd->prot_op = ses->prot_op;
>>  	scmd->eh_eflags = ses->eh_eflags;
>> diff --git a/include/scsi/scsi_eh.h b/include/scsi/scsi_eh.h
>> index 3810b340551c..9caa9b262a32 100644
>> --- a/include/scsi/scsi_eh.h
>> +++ b/include/scsi/scsi_eh.h
>> @@ -32,6 +32,7 @@ extern int scsi_ioctl_reset(struct scsi_device *, int __user *);
>>  struct scsi_eh_save {
>>  	/* saved state */
>>  	int result;
>> +	unsigned int resid;
> 
> There seems to be an inconsistency here. A signed int would be consistent 
> with the getter and setter helpers. Whereas, if you open-coded the 
> assignments instead, your unsigned int would make sense because 
> scsi_request.resid_len really is an unsigned int.

All fair points. Sending a V3. Thanks !


-- 
Damien Le Moal
Western Digital Research