Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 3.10 24/74] SCSI: sd: call blk_pm_runtime_init before add_disk | Date | Fri, 8 Nov 2013 22:51:29 -0800 |
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3.10-stable review patch. If anyone has any objections, please let me know.
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From: Aaron Lu <aaron.lu@intel.com>
commit 10c580e4239df5c3344ca00322eca86ab2de880b upstream.
Sujit has found a race condition that would make q->nr_pending unbalanced, it occurs as Sujit explained:
" sd_probe_async() -> add_disk() -> disk_add_event() -> schedule(disk_events_workfn) sd_revalidate_disk() blk_pm_runtime_init() return;
Let's say the disk_events_workfn() calls sd_check_events() which tries to send test_unit_ready() and because of sd_revalidate_disk() trying to send another commands the test_unit_ready() might be re-queued as the tagged command queuing is disabled.
So the race condition is -
Thread 1 | Thread 2 sd_revalidate_disk() | sd_check_events() ...nr_pending = 0 as q->dev = NULL| scsi_queue_insert() blk_runtime_pm_init() | blk_pm_requeue_request() -> | nr_pending = -1 since | q->dev != NULL "
The problem is, the test_unit_ready request doesn't get counted the first time it is queued, so the later decrement of q->nr_pending in blk_pm_requeue_request makes it unbalanced.
Fix this by calling blk_pm_runtime_init before add_disk so that all requests initiated there will all be counted.
Signed-off-by: Aaron Lu <aaron.lu@intel.com> Reported-and-tested-by: Sujit Reddy Thumma <sthumma@codeaurora.org> Signed-off-by: James Bottomley <JBottomley@Parallels.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- drivers/scsi/sd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/scsi/sd.c +++ b/drivers/scsi/sd.c @@ -2843,6 +2843,7 @@ static void sd_probe_async(void *data, a gd->events |= DISK_EVENT_MEDIA_CHANGE; } + blk_pm_runtime_init(sdp->request_queue, dev); add_disk(gd); if (sdkp->capacity) sd_dif_config_host(sdkp); @@ -2851,7 +2852,6 @@ static void sd_probe_async(void *data, a sd_printk(KERN_NOTICE, sdkp, "Attached SCSI %sdisk\n", sdp->removable ? "removable " : ""); - blk_pm_runtime_init(sdp->request_queue, dev); scsi_autopm_put_device(sdp); put_device(&sdkp->dev); }
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