diff options
| author | Tony Battersby <tonyb@cybernetics.com> | 2015-02-13 12:10:58 -0500 |
|---|---|---|
| committer | James Bottomley <JBottomley@Parallels.com> | 2015-02-17 06:57:54 -0800 |
| commit | 7772855a996ec6e16944b120ab5ce21050279821 (patch) | |
| tree | ee736c6d1316437299d0c6c4948cfbc02f1dff56 | |
| parent | 7568615c1054907ea8c7701ab86dad51aa099888 (diff) | |
sg: fix EWOULDBLOCK errors with scsi-mq
With scsi-mq enabled, userspace programs can get unexpected EWOULDBLOCK
(a.k.a. EAGAIN) errors when submitting commands to the SCSI generic
driver. Fix by calling blk_get_request() with GFP_KERNEL instead of
GFP_ATOMIC.
Note: to avoid introducing a potential deadlock, this patch should be
applied after the patch titled "sg: fix unkillable I/O wait deadlock
with scsi-mq".
Cc: <stable@vger.kernel.org> # 3.17+
Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Tested-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
| -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); |