Re: [RFC PATCH v2] scsi: fix oops in scsi_uninit_cmd()

[Bart Van Assche <bvanassche@acm.org>]

On Sat, 2019-03-16 at 10:09 +0800, Jason Yan wrote:
> If we remove the scsi disk when running io with fio, oops occured with
> the following condition.
> 
> [scsi_eh_0]                              [fio]
> scsi_end_request
>   ->blk_update_request
>     ->end_bio(io returned to userspace)
>                                          close
>                                            ->sd_release
>                                               ->scsi_disk_put
>                                                  ->scsi_disk_release
>                                                      ->disk->private_data = NULL;
> 
>   ->scsi_mq_uninit_cmd
>     ->scsi_uninit_cmd
>       ->scsi_cmd_to_driver
>     ->drv is NULL, Oops
> 
> There is a small window between blk_update_request() and
> scsi_mq_uninit_cmd() that scsi disk may have been released. This will
> cause a oops like below:
> 
> Unable to handle kernel NULL pointer dereference at virtual address
> 0000000000000000
> s/sync.c:67, func=xfer, error=In[11347.116050] Mem abort info:
> put/output error
> [11347.121598]   ESR = 0x96000006
> [11347.126200]   Exception class = DABT (current EL), IL = 32 bits
> [11347.132117]   SET = 0, FnV = 0
> [11347.135170]   EA = 0, S1PTW = 0
> [11347.138308] Data abort info:
> [11347.141186]   ISV = 0, ISS = 0x00000006
> [11347.145019]   CM = 0, WnR = 0
> [11347.147977] user pgtable: 4k pages, 48-bit VAs, pgdp =
> 00000000a67aece2
> [11347.154591] [0000000000000000] pgd=0000002f90774003,
> pud=0000002fab098003, pmd=0000000000000000
> [11347.163304] Internal error: Oops: 96000006 [#1] PREEMPT SMP
> [11347.168870] Modules linked in: hisi_sas_v3_hw hisi_sas_main libsas
> [11347.175044] CPU: 56 PID: 4294 Comm: scsi_eh_2 Not tainted
> 4.19.0-g8052059-dirty #2
> [11347.182600] Hardware name: Huawei D06/D06, BIOS Hisilicon D06 UEFI
> RC0 - B601 (V6.01) 11/08/2018
> [11347.191370] pstate: a0c00009 (NzCv daif 㰃繐ε흾㯗

Please verify whether the following patch is a valid alternative for your patch:

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index ed34bfbc3844..745ffdda1bc1 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -1408,6 +1408,7 @@ static void sd_release(struct gendisk *disk, fmode_t mode)
 {
 	struct scsi_disk *sdkp = scsi_disk(disk);
 	struct scsi_device *sdev = sdkp->device;
+	struct request_queue *q = sdkp->disk->queue;
 
 	SCSI_LOG_HLQUEUE(3, sd_printk(KERN_INFO, sdkp, "sd_release\n"));
 
@@ -1417,9 +1418,12 @@ static void sd_release(struct gendisk *disk, fmode_t mode)
 	}
 
 	/*
-	 * XXX and what if there are packets in flight and this close()
-	 * XXX is followed by a "rmmod sd_mod"?
+	 * Wait until any requests that are in progress have completed.
+	 * This is necessary to avoid that e.g. scsi_end_request() crashes
+	 * due to scsi_disk_relase() clearing the disk->private_data pointer.
 	 */
+	blk_mq_freeze_queue(q);
+	blk_mq_unfreeze_queue(q);
 
 	scsi_disk_put(sdkp);
 }

Thanks,

Bart.