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authorJörn Engel <joern@logfs.org>2012-04-12 17:33:58 -0400
committerJames Bottomley <JBottomley@Parallels.com>2012-05-17 10:08:54 +0100
commit6acddc5e911bb3a4a007448371ed7317c85669da (patch)
treeef5ac2ea141645723d2e898f83ed4414dc36f4bc /drivers/scsi/sg.c
parentebaf466be5afa6c6dca29005374de4534e0e6b33 (diff)
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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>
Diffstat (limited to 'drivers/scsi/sg.c')
-rw-r--r--drivers/scsi/sg.c16
1 files changed, 14 insertions, 2 deletions
diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 511e3ca1afd6..4a00364445f0 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -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 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 @@ sg_common_write(Sg_fd * sfp, Sg_request * srp,
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 @@ sg_ioctl(struct file *filp, unsigned int cmd_in, unsigned long arg)
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);