| Message ID | 1e722bb0ebc0c01867f6d79fa627e9310e7dbd87.1447361163.git.joseph.salisbury@canonical.com |
|---|---|
| State | New |
| Headers | show |
Positive test results. Seems low risk.
diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c index 9ad4116..787bc77 100644 --- a/drivers/scsi/scsi_sysfs.c +++ b/drivers/scsi/scsi_sysfs.c @@ -1067,6 +1067,14 @@ 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;
BugLink: http://bugs.launchpad.net/bugs/1509029 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. OriginalAuthor: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com> --- drivers/scsi/scsi_sysfs.c | 8 ++++++++ 1 file changed, 8 insertions(+)