diff options
Diffstat (limited to 'drivers/scsi/sg.c')
| -rw-r--r-- | drivers/scsi/sg.c | 17 |
1 files changed, 16 insertions, 1 deletions
diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c index 208bf3c8a16c..5cb2a5e80b2b 100644 --- a/drivers/scsi/sg.c +++ b/drivers/scsi/sg.c @@ -1680,7 +1680,22 @@ sg_start_req(Sg_request *srp, unsigned char *cmd) return -ENOMEM; } - rq = blk_get_request(q, rw, GFP_ATOMIC); + /* + * NOTE + * + * With scsi-mq enabled, there are a fixed number of preallocated + * requests equal in number to shost->can_queue. If all of the + * preallocated requests are already in use, then using GFP_ATOMIC with + * blk_get_request() will return -EWOULDBLOCK, whereas using GFP_KERNEL + * will cause blk_get_request() to sleep until an active command + * completes, freeing up a request. Neither option is ideal, but + * GFP_KERNEL is the better choice to prevent userspace from getting an + * unexpected EWOULDBLOCK. + * + * With scsi-mq disabled, blk_get_request() with GFP_KERNEL usually + * does not sleep except under memory pressure. + */ + rq = blk_get_request(q, rw, GFP_KERNEL); if (IS_ERR(rq)) { kfree(long_cmdp); return PTR_ERR(rq); |