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Date:   Tue, 10 Apr 2018 20:45:25 -0400
From:   Wakko Warner <wakko@animx.eu.org>
To:     Ming Lei <ming.lei@redhat.com>
Cc:     Bart Van Assche <Bart.VanAssche@wdc.com>,
        "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "richard.weinberger@gmail.com" <richard.weinberger@gmail.com>,
        "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Subject: Re: 4.15.14 crash with iscsi target and dvd
Message-ID: <20180411004525.GA9107@animx.eu.org>
References: <20180401182723.GA31755@animx.eu.org>
 <595a10cfb387e6b2ab4d2053b84fed9b3da9e079.camel@wdc.com>
 <20180406014644.GA16112@animx.eu.org>
 <20180406020651.GB16112@animx.eu.org>
 <fb0640c203409a84ab1bfbbc41078a5416138ad2.camel@wdc.com>
 <20180407165335.GA2515@animx.eu.org>
 <1ff8d234cc565ba9701ce31899fca5faa597e050.camel@wdc.com>
 <20180408160254.GA22869@animx.eu.org>
 <f9467e78ce05446e7a89f06713c36fb638d1b6ad.camel@wdc.com>
 <20180409233436.GC6450@ming.t460p>
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Ming Lei wrote:
> Sure, thanks for your sharing.
> 
> Wakko, could you test the following patch and see if there is any
> difference?
> 
> --
> diff --git a/drivers/target/target_core_pscsi.c b/drivers/target/target_core_pscsi.c
> index 0d99b242e82e..6147178f1f37 100644
> --- a/drivers/target/target_core_pscsi.c
> +++ b/drivers/target/target_core_pscsi.c
> @@ -888,7 +888,7 @@ pscsi_map_sg(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
>  		if (len > 0 && data_len > 0) {
>  			bytes = min_t(unsigned int, len, PAGE_SIZE - off);
>  			bytes = min(bytes, data_len);
> -
> + new_bio:
>  			if (!bio) {
>  				nr_vecs = min_t(int, BIO_MAX_PAGES, nr_pages);
>  				nr_pages -= nr_vecs;
> @@ -931,6 +931,7 @@ pscsi_map_sg(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
>  				 * be allocated with pscsi_get_bio() above.
>  				 */
>  				bio = NULL;
> +				goto new_bio;
>  			}
>  
>  			data_len -= bytes;

Sorry for the delay.  I reverted my change, added this one.  I didn't
reboot, I just unloaded and loaded this one.
Note: /dev/sr1 as seen from the initiator is /dev/sr0 (physical disc) on the
target.

Doesn't crash, however on the initiator I see this:
[9273849.707777] ISO 9660 Extensions: RRIP_1991A
[9273863.359718] scsi_io_completion: 13 callbacks suppressed
[9273863.359788] sr 26:0:0:0: [sr1] tag#1 UNKNOWN(0x2003) Result: hostbyte=0x00 driverbyte=0x08
[9273863.359909] sr 26:0:0:0: [sr1] tag#1 Sense Key : 0x2 [current] 
[9273863.359974] sr 26:0:0:0: [sr1] tag#1 ASC=0x8 ASCQ=0x0 
[9273863.360036] sr 26:0:0:0: [sr1] tag#1 CDB: opcode=0x28 28 00 00 22 f6 96 00 00 80 00
[9273863.360116] blk_update_request: 13 callbacks suppressed
[9273863.360177] blk_update_request: I/O error, dev sr1, sector 9165400
[9273875.864648] sr 26:0:0:0: [sr1] tag#1 UNKNOWN(0x2003) Result: hostbyte=0x00 driverbyte=0x08
[9273875.864738] sr 26:0:0:0: [sr1] tag#1 Sense Key : 0x2 [current] 
[9273875.864801] sr 26:0:0:0: [sr1] tag#1 ASC=0x8 ASCQ=0x0 
[9273875.864890] sr 26:0:0:0: [sr1] tag#1 CDB: opcode=0x28 28 00 00 22 f7 16 00 00 80 00
[9273875.864971] blk_update_request: I/O error, dev sr1, sector 9165912

To cause this, I mounted the dvd as seen in the first line and ran this
command: find /cdrom2 -type f | xargs -tn1 cat > /dev/null
I did some various tests.  Each test was done after umount and mount to
clear the cache.
cat <file> > /dev/null causes the message.
dd if=<file> of=/dev/null bs=2048 doesn't
	using bs=4096 doesn't
	using bs=64k doesn't
	using bs=128k does
cat uses a blocksize of 128k.

The following was done without being mounted.
ddrescue -f -f /dev/sr1 /dev/null 
	doesn't cause the message
dd if=/dev/sr1 of=/dev/null bs=128k
	doesn't cause the message
using bs=256k causes the message once:
[9275916.857409] sr 27:0:0:0: [sr1] tag#0 UNKNOWN(0x2003) Result: hostbyte=0x00 driverbyte=0x08
[9275916.857482] sr 27:0:0:0: [sr1] tag#0 Sense Key : 0x2 [current] 
[9275916.857520] sr 27:0:0:0: [sr1] tag#0 ASC=0x8 ASCQ=0x0 
[9275916.857556] sr 27:0:0:0: [sr1] tag#0 CDB: opcode=0x28 28 00 00 00 00 00 00 00 80 00
[9275916.857614] blk_update_request: I/O error, dev sr1, sector 0

If I access the disc from the target natively either by mounting and
accessing files or working with the device directly (ie dd) no errors are
logged on the target.

-- 
 Microsoft has beaten Volkswagen's world record.  Volkswagen only created 22
 million bugs.