scsi: core: save/restore command resid for error handling

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.

Fix this problem by saving the original command residual 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 the residual to 0 in scsi_eh_prep_cmnd() after saving the original
command value in struct scsi_eh_save.

Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20191001074839.1994-1-damien.lemoal@wdc.com
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

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_len = scmd->req.resid_len;
 	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;
+	scmd->req.resid_len = 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;
+	scmd->req.resid_len = ses->resid_len;
 	scmd->underflow = ses->underflow;
 	scmd->prot_op = ses->prot_op;
 	scmd->eh_eflags = ses->eh_eflags;

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_len;
 	int eh_eflags;
 	enum dma_data_direction data_direction;
 	unsigned underflow;