On 10/22/2015 10:12 AM, Vitaly Kuznetsov wrote:
On some host errors storvsc module tries to remove sdev by scheduling a job
which does the following:
sdev = scsi_device_lookup(wrk->host, 0, 0, wrk->lun);
if (sdev) {
scsi_remove_device(sdev);
scsi_device_put(sdev);
}
While this code seems correct the following crash is observed:
general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC
RIP: 0010:[<ffffffff81169979>] [<ffffffff81169979>] bdi_destroy+0x39/0x220
...
[<ffffffff814aecdc>] ? _raw_spin_unlock_irq+0x2c/0x40
[<ffffffff8127b7db>] blk_cleanup_queue+0x17b/0x270
[<ffffffffa00b54c4>] __scsi_remove_device+0x54/0xd0 [scsi_mod]
[<ffffffffa00b556b>] scsi_remove_device+0x2b/0x40 [scsi_mod]
[<ffffffffa00ec47d>] storvsc_remove_lun+0x3d/0x60 [hv_storvsc]
[<ffffffff81080791>] process_one_work+0x1b1/0x530
...
The problem comes with the fact that many such jobs (for the same device)
are being scheduled simultaneously. While scsi_remove_device() uses
shost->scan_mutex and scsi_device_lookup() will fail for a device in
SDEV_DEL state there is no protection against someone who did
scsi_device_lookup() before we actually entered __scsi_remove_device(). So
the whole scenario looks like that: two callers do simultaneous (or
preemption happens) calls to scsi_device_lookup() ant these calls succeed
for all of them, after that both callers try doing scsi_remove_device().
shost->scan_mutex only serializes their calls to __scsi_remove_device()
and we end up doing the cleanup path twice.
Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com>
---
drivers/scsi/scsi_sysfs.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index b333389..e0d2707 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -1076,6 +1076,14 @@ void __scsi_remove_device(struct scsi_device *sdev)
{
struct device *dev = &sdev->sdev_gendev;
+ /*
+ * This cleanup path is not reentrant and while it is impossible
+ * to get a new reference with scsi_device_get() someone can still
+ * hold a previously acquired one.
+ */
+ if (sdev->sdev_state == SDEV_DEL)
+ return;
+
if (sdev->is_visible) {
if (scsi_device_set_state(sdev, SDEV_CANCEL) != 0)
return;
Hello Vitaly,
Sorry but I don't see how the above patch could be a proper fix. If two
calls to __scsi_remove_device() occur concurrently the crash explained
above can still occur. The storsvc driver should be modified such that
concurrent __scsi_remove_device() calls do not occur. How about
preventing concurrent calls via a mutex ? Another possible approach is
to use the workqueue mechanism. An example can be found in the SRP
initiator driver (ib_srp).
Bart.
--
To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
