[SCSI] sg: prevent unwoken sleep
srp->done is protected by sfp->rq_list_lock everywhere, except for this
one case. Result can be that the wake-up happens before the cacheline
with the changed srp->done has arrived, so the waiter can go back to
sleep and never be woken up again.
The wait_event_interruptible() means that anyone trying to debug this
unlikely race will likely notice everything working fine again, as the
next signal will unwedge things. Evil.
Signed-off-by: Joern Engel <joern@logfs.org>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 511e3ca..4a003644 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -137,7 +137,8 @@
char res_used; /* 1 -> using reserve buffer, 0 -> not ... */
char orphan; /* 1 -> drop on sight, 0 -> normal */
char sg_io_owned; /* 1 -> packet belongs to SG_IO */
- volatile char done; /* 0->before bh, 1->before read, 2->read */
+ /* done protected by rq_list_lock */
+ char done; /* 0->before bh, 1->before read, 2->read */
struct request *rq;
struct bio *bio;
struct execute_work ew;
@@ -760,6 +761,17 @@
return 0;
}
+static int srp_done(Sg_fd *sfp, Sg_request *srp)
+{
+ unsigned long flags;
+ int ret;
+
+ read_lock_irqsave(&sfp->rq_list_lock, flags);
+ ret = srp->done;
+ read_unlock_irqrestore(&sfp->rq_list_lock, flags);
+ return ret;
+}
+
static int
sg_ioctl(struct file *filp, unsigned int cmd_in, unsigned long arg)
{
@@ -791,7 +803,7 @@
if (result < 0)
return result;
result = wait_event_interruptible(sfp->read_wait,
- (srp->done || sdp->detached));
+ (srp_done(sfp, srp) || sdp->detached));
if (sdp->detached)
return -ENODEV;
write_lock_irq(&sfp->rq_list_lock);
