On 06/23/2014 03:59 PM, Christoph Hellwig wrote:
> This patch causes a regression when using the iscsi initiator over
> TCP for me. When mounting a newly created ext4 filesystem I get the
> following BUG:
>
> [ 31.611803] BUG: unable to handle kernel NULL pointer dereference at 000000000000000c
> [ 31.613563] IP: [<ffffffff8197b38d>] iscsi_tcp_segment_done+0x2bd/0x380
> [ 31.613563] PGD 7a3e4067 PUD 7a45f067 PMD 0
> [ 31.613563] Oops: 0000 [#1] SMP
> [ 31.613563] Modules linked in:
> [ 31.613563] CPU: 3 PID: 3739 Comm: kworker/u8:5 Not tainted 3.16.0-rc2 #187
> [ 31.613563] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
> [ 31.613563] Workqueue: iscsi_q_2 iscsi_xmitworker
> [ 31.613563] task: ffff88007b33cf10 ti: ffff88007ad94000 task.ti: ffff88007ad94000
> [ 31.613563] RIP: 0010:[<ffffffff8197b38d>] [<ffffffff8197b38d>] iscsi_tcp_segment_done+0x2bd/0x380
> [ 31.613563] RSP: 0018:ffff88007ad97b38 EFLAGS: 00010246
> [ 31.613563] RAX: 0000000000000000 RBX: ffff88007cd67910 RCX: 0000000000000200
> [ 31.613563] RDX: 0000000000002000 RSI: 0000000000000000 RDI: ffff88007cd67910
> [ 31.613563] RBP: ffff88007ad97b98 R08: 0000000000000200 R09: 0000000000000000
> [ 31.613563] R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000
> [ 31.613563] R13: ffff88007cd67780 R14: 0000000000000000 R15: 0000000000000000
> [ 31.613563] FS: 0000000000000000(0000) GS:ffff88007fd80000(0000) knlGS:0000000000000000
> [ 31.613563] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> [ 31.613563] CR2: 000000000000000c CR3: 000000007afd9000 CR4: 00000000000006e0
> [ 31.613563] Stack:
> [ 31.613563] ffff88007ad97b98 ffffffff81c68fd6 ffffffff81c68f20 ffff88007c8e37c8
> [ 31.613563] 000000007b33d728 ffff88007dc805b0 ffff88007ad97c58 0000000000000200
> [ 31.613563] ffff88007cd67780 ffff880000c00040 ffff88007ad97c00 ffff88007cd67910
> [ 31.613563] Call Trace:
> [ 31.613563] [<ffffffff81c68fd6>] ? inet_sendpage+0xb6/0x130
> [ 31.613563] [<ffffffff81c68f20>] ? inet_dgram_connect+0x80/0x80
> [ 31.613563] [<ffffffff8197bd95>] iscsi_sw_tcp_pdu_xmit+0xe5/0x2e0
> [ 31.613563] [<ffffffff8197badf>] ? iscsi_sw_tcp_pdu_init+0x1bf/0x390
> [ 31.613563] [<ffffffff81979b82>] iscsi_tcp_task_xmit+0xa2/0x2b0
> [ 31.613563] [<ffffffff81974815>] ? iscsi_xmit_task+0x45/0xd0
> [ 31.613563] [<ffffffff810fbb8d>] ? trace_hardirqs_on+0xd/0x10
> [ 31.613563] [<ffffffff810b54a0>] ? __local_bh_enable_ip+0x70/0xd0
> [ 31.613563] [<ffffffff81974829>] iscsi_xmit_task+0x59/0xd0
> [ 31.613563] [<ffffffff81978468>] iscsi_xmitworker+0x288/0x330
> [ 31.613563] [<ffffffff810cc847>] process_one_work+0x1c7/0x490
> [ 31.613563] [<ffffffff810cc7dd>] ? process_one_work+0x15d/0x490
> [ 31.613563] [<ffffffff810cd539>] worker_thread+0x119/0x4f0
> [ 31.613563] [<ffffffff810fbb8d>] ? trace_hardirqs_on+0xd/0x10
> [ 31.613563] [<ffffffff810cd420>] ? init_pwq+0x190/0x190
> [ 31.613563] [<ffffffff810d3c3f>] kthread+0xdf/0x100
> [ 31.613563] [<ffffffff810d3b60>] ? __init_kthread_worker+0x70/0x70
> [ 31.613563] [<ffffffff81d904bc>] ret_from_fork+0x7c/0xb0
> [ 31.613563] [<ffffffff810d3b60>] ? __init_kthread_worker+0x70/0x70
> [ 31.613563] Code: 89 03 31 c0 e9 cc fe ff ff 0f 1f 44 00 00 48 8b 7b
> 30 e8 17 74 de ff 8b 53 10 c7 43 40 00 00 00 00 48 89 43 30 44 89 f6 48
> 89 df <8b> 40 0c 48 c7 03 00 00 00 00 2b 53 14 39 c2 0f 47 d0 89 53 08
>
>
> (gdb) l *(iscsi_tcp_segment_done+0x2bd)
> 0xffffffff8197b38d 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
>
Ok, it looks like scsi_out(scsi_cmnd)->length (iscsi_tcp/libiscsi_tcp
still uses that for lower level operations since it was not converted to
support t10 pi) returns a different value than scsi_transfer_length()
(libiscsi uses this for higher level operations when it was converted to
t10 support since iser uses that module and also has t10 support) for
some commands. We then end up incorrectly thinking some requests are the
wrong size and then hit this. Looking into why exactly this happens.
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