| Message ID | 1447938139-22072-1-git-send-email-vkuznets@redhat.com (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
This looks fine to me. I wonder why we even bother returning
deleted devices for a normal scsi_device_lookup, but let's get
this isolated fix in for now and sort out the big picture later.
Reviewed-by: Christoph Hellwig <hch@lst.de>
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>>>>> "Vitaly" == Vitaly Kuznetsov <vkuznets@redhat.com> writes:
Vitaly> On some host errors storvsc module tries to remove sdev by
Vitaly> scheduling a job which does the following:
Applied to 4.4.
diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c index 8d23122..905dd1c 100644 --- a/drivers/scsi/scsi_sysfs.c +++ b/drivers/scsi/scsi_sysfs.c @@ -1102,6 +1102,14 @@ 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;
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 both of them, after that they 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 <vkuznets@redhat.com> --- drivers/scsi/scsi_sysfs.c | 8 ++++++++ 1 file changed, 8 insertions(+)