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[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>
This commit is contained in:
Jörn Engel 2012-04-12 17:33:58 -04:00 committed by James Bottomley
parent ebaf466be5
commit 6acddc5e91
1 changed files with 14 additions and 2 deletions
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16
drivers/scsi/sg.c
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@ -137,7 +137,8 @@ typedef struct sg_request { /* SG_MAX_QUEUE requests outstanding per file */
char res_used; /* 1 -> using reserve buffer, 0 -> not ... */ char res_used; /* 1 -> using reserve buffer, 0 -> not ... */
char orphan; /* 1 -> drop on sight, 0 -> normal */ char orphan; /* 1 -> drop on sight, 0 -> normal */
char sg_io_owned; /* 1 -> packet belongs to SG_IO */ 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 request *rq;
struct bio *bio; struct bio *bio;
struct execute_work ew; struct execute_work ew;
@ -760,6 +761,17 @@ sg_common_write(Sg_fd * sfp, Sg_request * srp,
return 0; 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 static int
sg_ioctl(struct file *filp, unsigned int cmd_in, unsigned long arg) sg_ioctl(struct file *filp, unsigned int cmd_in, unsigned long arg)
{ {
@ -791,7 +803,7 @@ sg_ioctl(struct file *filp, unsigned int cmd_in, unsigned long arg)
if (result < 0) if (result < 0)
return result; return result;
result = wait_event_interruptible(sfp->read_wait, result = wait_event_interruptible(sfp->read_wait,
(srp->done || sdp->detached)); (srp_done(sfp, srp) || sdp->detached));
if (sdp->detached) if (sdp->detached)
return -ENODEV; return -ENODEV;
write_lock_irq(&sfp->rq_list_lock); write_lock_irq(&sfp->rq_list_lock);