From: Michael Kelley mikelley@microsoft.com
commit 175544ad48cbf56affeef2a679c6a4d4fb1e2881 upstream.
Hyper-V provides the ability to connect Fibre Channel LUNs to the host system and present them in a guest VM as a SCSI device. I/O to the vFC device is handled by the storvsc driver. The storvsc driver includes a partial integration with the FC transport implemented in the generic portion of the Linux SCSI subsystem so that FC attributes can be displayed in /sys. However, the partial integration means that some aspects of vFC don't work properly. Unfortunately, a full and correct integration isn't practical because of limitations in what Hyper-V provides to the guest.
In particular, in the context of Hyper-V storvsc, the FC transport timeout function fc_eh_timed_out() causes a kernel panic because it can't find the rport and dereferences a NULL pointer. The original patch that added the call from storvsc_eh_timed_out() to fc_eh_timed_out() is faulty in this regard.
In many cases a timeout is due to a transient condition, so the situation can be improved by just continuing to wait like with other I/O requests issued by storvsc, and avoiding the guaranteed panic. For a permanent failure, continuing to wait may result in a hung thread instead of a panic, which again may be better.
So fix the panic by removing the storvsc call to fc_eh_timed_out(). This allows storvsc to keep waiting for a response. The change has been tested by users who experienced a panic in fc_eh_timed_out() due to transient timeouts, and it solves their problem.
In the future we may want to deprecate the vFC functionality in storvsc since it can't be fully fixed. But it has current users for whom it is working well enough, so it should probably stay for a while longer.
Fixes: 3930d7309807 ("scsi: storvsc: use default I/O timeout handler for FC devices") Cc: stable@vger.kernel.org Signed-off-by: Michael Kelley mikelley@microsoft.com Link: https://lore.kernel.org/r/1690606764-79669-1-git-send-email-mikelley@microso... Signed-off-by: Martin K. Petersen martin.petersen@oracle.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/scsi/storvsc_drv.c | 4 ---- 1 file changed, 4 deletions(-)
--- a/drivers/scsi/storvsc_drv.c +++ b/drivers/scsi/storvsc_drv.c @@ -1505,10 +1505,6 @@ static int storvsc_host_reset_handler(st */ static enum blk_eh_timer_return storvsc_eh_timed_out(struct scsi_cmnd *scmnd) { -#if IS_ENABLED(CONFIG_SCSI_FC_ATTRS) - if (scmnd->device->host->transportt == fc_transport_template) - return fc_eh_timed_out(scmnd); -#endif return BLK_EH_RESET_TIMER; }