diff options
| author | Tony Battersby <tonyb@cybernetics.com> | 2015-02-13 18:09:44 +0100 |
|---|---|---|
| committer | James Bottomley <JBottomley@Parallels.com> | 2015-02-17 15:55:32 +0100 |
| commit | 7568615c1054907ea8c7701ab86dad51aa099888 (patch) | |
| tree | 9a8fbf348961fd4970423b51a41ce7ae7b3e0421 /drivers | |
| parent | sg: fix read() error reporting (diff) | |
| download | linux-7568615c1054907ea8c7701ab86dad51aa099888.tar.xz linux-7568615c1054907ea8c7701ab86dad51aa099888.zip | |
sg: fix unkillable I/O wait deadlock with scsi-mq
When using the write()/read() interface for submitting commands, the
SCSI generic driver does not call blk_put_request() on a completed SCSI
command until userspace calls read() to get the command completion.
Since scsi-mq uses a fixed number of preallocated requests, this makes
it possible for userspace to exhaust the entire preallocated supply of
requests. For places in the kernel that call blk_get_request() with
GFP_KERNEL, this can cause the calling process to deadlock in a
permanent unkillable I/O wait in blk_get_request() -> ... -> bt_get().
For places in the kernel that call blk_get_request() with GFP_ATOMIC,
this can cause blk_get_request() always to return -EWOULDBLOCK. Note
that these problems happen only if scsi-mq is enabled. Prevent the
problems by calling blk_put_request() as soon as the SCSI command
completes instead of waiting for userspace to call read().
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>
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/scsi/sg.c | 17 |
1 files changed, 14 insertions, 3 deletions
diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c index 6ad1480e87b7..208bf3c8a16c 100644 --- a/drivers/scsi/sg.c +++ b/drivers/scsi/sg.c @@ -1335,6 +1335,17 @@ sg_rq_end_io(struct request *rq, int uptodate) } /* Rely on write phase to clean out srp status values, so no "else" */ + /* + * Free the request as soon as it is complete so that its resources + * can be reused without waiting for userspace to read() the + * result. But keep the associated bio (if any) around until + * blk_rq_unmap_user() can be called from user context. + */ + srp->rq = NULL; + if (rq->cmd != rq->__cmd) + kfree(rq->cmd); + __blk_put_request(rq->q, rq); + write_lock_irqsave(&sfp->rq_list_lock, iflags); if (unlikely(srp->orphan)) { if (sfp->keep_orphan) @@ -1762,10 +1773,10 @@ sg_finish_rem_req(Sg_request *srp) SCSI_LOG_TIMEOUT(4, sg_printk(KERN_INFO, sfp->parentdp, "sg_finish_rem_req: res_used=%d\n", (int) srp->res_used)); - if (srp->rq) { - if (srp->bio) - ret = blk_rq_unmap_user(srp->bio); + if (srp->bio) + ret = blk_rq_unmap_user(srp->bio); + if (srp->rq) { if (srp->rq->cmd != srp->rq->__cmd) kfree(srp->rq->cmd); blk_put_request(srp->rq); |