Date: Thu, 15 Dec 2016 09:29:53 +1100
From: Dave Chinner <david@fromorbit.com>
To: linux-kernel@vger.kernel.org
Cc: Lee Duncan <lduncan@suse.com>, Chris Leech <cleech@redhat.com>,
        open-iscsi@googlegroups.com
Subject: Re: [4.10, panic, regression] iscsi: null pointer deref at
 iscsi_tcp_segment_done+0x20d/0x2e0
Message-ID: <20161214222953.GI4326@dastard>
References: <20161214222411.GH4326@dastard>
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On Thu, Dec 15, 2016 at 09:24:11AM +1100, Dave Chinner wrote:
> Hi folks,
> 
> Just updated my test boxes from 4.9 to a current Linus 4.10 merge
> window kernel to test the XFS merge I am preparing for Linus.
> Unfortunately, all my test VMs using iscsi failed pretty much
> instantly on the first mount of an iscsi device:
> 
> [  159.372704] XFS (sdb): EXPERIMENTAL reverse mapping btree feature enabled. Use at your own risk!
> [  159.374612] XFS (sdb): Mounting V5 Filesystem
> [  159.425710] XFS (sdb): Ending clean mount
> [  160.274438] BUG: unable to handle kernel NULL pointer dereference at 000000000000000c
> [  160.275851] IP: iscsi_tcp_segment_done+0x20d/0x2e0

FYI, crash is here:

(gdb) l *(iscsi_tcp_segment_done+0x20d)
0xffffffff81b950bd is in iscsi_tcp_segment_done (drivers/scsi/libiscsi_tcp.c:102).
97	iscsi_tcp_segment_init_sg(struct iscsi_segment *segment,
98				  struct scatterlist *sg, unsigned int offset)
99	{
100		segment->sg = sg;
101		segment->sg_offset = offset;
102		segment->size = min(sg->length - offset,
103				    segment->total_size - segment->total_copied);
104		segment->data = NULL;
105	}
106	

So it looks to be sg = NULL, which means there's probably an issue
with the scatterlist...

-Dave.

> [  160.276565] PGD 336ed067 [  160.276885] PUD 31b0d067
> PMD 0 [  160.277309]
> [  160.277523] Oops: 0000 [#1] PREEMPT SMP
> [  160.278004] Modules linked in:
> [  160.278407] CPU: 0 PID: 16 Comm: kworker/u2:1 Not tainted 4.9.0-dgc #18
> [  160.279224] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Debian-1.8.2-1 04/01/2014
> [  160.280314] Workqueue: iscsi_q_2 iscsi_xmitworker
> [  160.280919] task: ffff88003e280000 task.stack: ffffc90000080000
> [  160.281647] RIP: 0010:iscsi_tcp_segment_done+0x20d/0x2e0
> [  160.282312] RSP: 0018:ffffc90000083c38 EFLAGS: 00010206
> [  160.282980] RAX: 0000000000000000 RBX: ffff880039061730 RCX: 0000000000000000
> [  160.283854] RDX: 0000000000001e00 RSI: 0000000000000000 RDI: ffff880039061730
> [  160.284738] RBP: ffffc90000083c90 R08: 0000000000000200 R09: 00000000000005a8
> [  160.285627] R10: 000000009835607d R11: 0000000000000000 R12: 0000000000000200
> [  160.286495] R13: 0000000000000000 R14: ffff8800390615a0 R15: ffff880039061730
> [  160.287362] FS:  0000000000000000(0000) GS:ffff88003fc00000(0000) knlGS:0000000000000000
> [  160.288340] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  160.289113] CR2: 000000000000000c CR3: 0000000031a8d000 CR4: 00000000000006f0
> [  160.290084] Call Trace:
> [  160.290429]  ? inet_sendpage+0x4d/0x140
> [  160.290957]  iscsi_sw_tcp_xmit_segment+0x89/0x110
> [  160.291597]  iscsi_sw_tcp_pdu_xmit+0x56/0x180
> [  160.292190]  iscsi_tcp_task_xmit+0xb8/0x280
> [  160.292771]  iscsi_xmit_task+0x53/0xc0
> [  160.293282]  iscsi_xmitworker+0x274/0x310
> [  160.293835]  process_one_work+0x1de/0x4d0
> [  160.294388]  worker_thread+0x4b/0x4f0
> [  160.294889]  kthread+0x10c/0x140
> [  160.295333]  ? process_one_work+0x4d0/0x4d0
> [  160.295898]  ? kthread_create_on_node+0x40/0x40
> [  160.296525]  ret_from_fork+0x25/0x30
> [  160.297015] Code: 43 18 00 00 00 00 e9 ad fe ff ff 48 8b 7b 30 e8 da e7 ca ff 8b 53 10 44 89 ee 48 89 df 2b 53 14 48 89 43 30 c7 43 40 00 00 00 00 <8b
> [  160.300674] RIP: iscsi_tcp_segment_done+0x20d/0x2e0 RSP: ffffc90000083c38
> [  160.301584] CR2: 000000000000000c
> 
> 
> Known problem, or something new?
> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com
> 

-- 
Dave Chinner
david@fromorbit.com