scsi_debug: fix sleep in invalid context

In this post: http://www.spinics.net/lists/linux-scsi/msg97124.html the
author shows some kernel infrastructure complaining about a sleep in an
invalid context. Remove offending call to vmalloc().  Instead of using
kzalloc() which reviewers didn't like, use a bucket system (64 bytes on
the stack) and potentially multiple calls to sg_pcopy_from_buffer() to
construct the 'data-in' buffer for the SCSI REPORT LUNS command.

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
Acked-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index 0f9ba41..6a219a0 100644 (file)
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -890,7 +890,7 @@ static int make_ua(struct scsi_cmnd *scp, struct sdebug_dev_info *devip)
        return 0;
 }
 
-/* Returns 0 if ok else (DID_ERROR << 16). Sets scp->resid . */
+/* Build SCSI "data-in" buffer. Returns 0 if ok else (DID_ERROR << 16). */
 static int fill_from_dev_buffer(struct scsi_cmnd *scp, unsigned char *arr,
                                int arr_len)
 {
@@ -909,7 +909,35 @@ static int fill_from_dev_buffer(struct scsi_cmnd *scp, unsigned char *arr,
        return 0;
 }
 
-/* Returns number of bytes fetched into 'arr' or -1 if error. */
+/* Partial build of SCSI "data-in" buffer. Returns 0 if ok else
+ * (DID_ERROR << 16). Can write to offset in data-in buffer. If multiple
+ * calls, not required to write in ascending offset order. Assumes resid
+ * set to scsi_bufflen() prior to any calls.
+ */
+static int p_fill_from_dev_buffer(struct scsi_cmnd *scp, const void *arr,
+                                 int arr_len, unsigned int off_dst)
+{
+       int act_len, n;
+       struct scsi_data_buffer *sdb = scsi_in(scp);
+       off_t skip = off_dst;
+
+       if (sdb->length <= off_dst)
+               return 0;
+       if (!(scsi_bidi_cmnd(scp) || scp->sc_data_direction == DMA_FROM_DEVICE))
+               return DID_ERROR << 16;
+
+       act_len = sg_pcopy_from_buffer(sdb->table.sgl, sdb->table.nents,
+                                      arr, arr_len, skip);
+       pr_debug("%s: off_dst=%u, scsi_bufflen=%u, act_len=%u, resid=%d\n",
+                __func__, off_dst, scsi_bufflen(scp), act_len, sdb->resid);
+       n = (int)scsi_bufflen(scp) - ((int)off_dst + act_len);
+       sdb->resid = min(sdb->resid, n);
+       return 0;
+}
+
+/* Fetches from SCSI "data-out" buffer. Returns number of bytes fetched into
+ * 'arr' or -1 if error.
+ */
 static int fetch_to_dev_buffer(struct scsi_cmnd *scp, unsigned char *arr,
                               int arr_len)
 {
@@ -3269,6 +3297,8 @@ static int resp_get_lba_status(struct scsi_cmnd *scp,
        return fill_from_dev_buffer(scp, arr, SDEBUG_GET_LBA_STATUS_LEN);
 }
 
+#define RL_BUCKET_ELEMS 8
+
 /* Even though each pseudo target has a REPORT LUNS "well known logical unit"
  * (W-LUN), the normal Linux scanning logic does not associate it with a
  * device (e.g. /dev/sg7). The following magic will make that association:
@@ -3285,12 +3315,14 @@ static int resp_report_luns(struct scsi_cmnd *scp,
        unsigned char select_report;
        u64 lun;
        struct scsi_lun *lun_p;
-       u8 *arr;
+       u8 arr[RL_BUCKET_ELEMS * sizeof(struct scsi_lun)];
        unsigned int lun_cnt;   /* normal LUN count (max: 256) */
        unsigned int wlun_cnt;  /* report luns W-LUN count */
        unsigned int tlun_cnt;  /* total LUN count */
        unsigned int rlen;      /* response length (in bytes) */
-       int i, res;
+       int k, j, n, res;
+       unsigned int off_rsp = 0;
+       const int sz_lun = sizeof(struct scsi_lun);
 
        clear_luns_changed_on_target(devip);
 
@@ -3329,33 +3361,40 @@ static int resp_report_luns(struct scsi_cmnd *scp,
                --lun_cnt;
 
        tlun_cnt = lun_cnt + wlun_cnt;
-
-       rlen = (tlun_cnt * sizeof(struct scsi_lun)) + 8;
-       arr = vmalloc(rlen);
-       if (!arr) {
-               mk_sense_buffer(scp, ILLEGAL_REQUEST, INSUFF_RES_ASC,
-                               INSUFF_RES_ASCQ);
-               return check_condition_result;
-       }
-       memset(arr, 0, rlen);
+       rlen = tlun_cnt * sz_lun;       /* excluding 8 byte header */
+       scsi_set_resid(scp, scsi_bufflen(scp));
        pr_debug("select_report %d luns = %d wluns = %d no_lun0 %d\n",
                 select_report, lun_cnt, wlun_cnt, sdebug_no_lun_0);
 
-       /* luns start at byte 8 in response following the header */
-       lun_p = (struct scsi_lun *)&arr[8];
-
-       /* LUNs use single level peripheral device addressing method */
+       /* loops rely on sizeof response header same as sizeof lun (both 8) */
        lun = sdebug_no_lun_0 ? 1 : 0;
-       for (i = 0; i < lun_cnt; i++)
-               int_to_scsilun(lun++, lun_p++);
-
-       if (wlun_cnt)
-               int_to_scsilun(SCSI_W_LUN_REPORT_LUNS, lun_p++);
-
-       put_unaligned_be32(rlen - 8, &arr[0]);
-
-       res = fill_from_dev_buffer(scp, arr, rlen);
-       vfree(arr);
+       for (k = 0, j = 0, res = 0; true; ++k, j = 0) {
+               memset(arr, 0, sizeof(arr));
+               lun_p = (struct scsi_lun *)&arr[0];
+               if (k == 0) {
+                       put_unaligned_be32(rlen, &arr[0]);
+                       ++lun_p;
+                       j = 1;
+               }
+               for ( ; j < RL_BUCKET_ELEMS; ++j, ++lun_p) {
+                       if ((k * RL_BUCKET_ELEMS) + j > lun_cnt)
+                               break;
+                       int_to_scsilun(lun++, lun_p);
+               }
+               if (j < RL_BUCKET_ELEMS)
+                       break;
+               n = j * sz_lun;
+               res = p_fill_from_dev_buffer(scp, arr, n, off_rsp);
+               if (res)
+                       return res;
+               off_rsp += n;
+       }
+       if (wlun_cnt) {
+               int_to_scsilun(SCSI_W_LUN_REPORT_LUNS, lun_p);
+               ++j;
+       }
+       if (j > 0)
+               res = p_fill_from_dev_buffer(scp, arr, j * sz_lun, off_rsp);
        return res;
 }