On 21.02.2016 22:09, John David Anglin wrote:
> On 2016-02-21, at 3:28 PM, James Bottomley wrote:
>
>> That said, I still can't reproduce this, so you're going to have to
>> help me find it. Current theory is ll_merge_request_fn() it looks like
>> there's scope for miscalculation in there. Can you instrument this
>> line
>>
>> /* Merge is OK... */
>> req->nr_phys_segments = total_phys_segments;
>>
>> To add just before the return
>>
>> if (req->nr_phys_segments != __blk_recalc_rq_segments(rq->q, rq->bio, false)
>> printk("MISMATCH IN MERGE: got %d, should get %d\n",
>> req->nr_phys_segments,
>> __blk_recalc_rq_segments(rq->q, rq->bio, false));
>
> This didn't trigger. There were some typos:
It didn't trigger for me either.
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index d9c3a75..e8969ef 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -545,6 +545,12 @@ static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
>
> /* Merge is OK... */
> req->nr_phys_segments = total_phys_segments;
> +
> +if (req->nr_phys_segments != __blk_recalc_rq_segments(req->q, req->bio, false))
> + printk("MISMATCH IN MERGE: got %d, should get %d\n",
> + req->nr_phys_segments,
> + __blk_recalc_rq_segments(req->q, req->bio, false));
> +
> return 1;
> }
Interestingly it now triggered somewhere else...
I enabled CONFIG_DEBUG_SG, which I had enabled the last few times as well, but it now happened
for the first time:
[ 49.848000] scsi_init_sgtable: nr_phys_segments = 4
[ 49.848000] NEW SEGMENT sg = 00000000bbdd5008!!!
[ 49.848000] __blk_segment_map_sg: length = 65536, nbytes = 4096, sum = 69632 > 65536
[ 49.848000] __blk_segment_map_sg: BIOVEC_PHYS_MERGEABLE = 1, BIOVEC_SEG_BOUNDARY = 1
[ 49.848000] NEW SEGMENT sg = 00000000bbdd5008!!!
[ 49.848000] __blk_segment_map_sg: length = 8192, nbytes = 4096, sum = 12288 > 65536
[ 49.848000] __blk_segment_map_sg: BIOVEC_PHYS_MERGEABLE = 0, BIOVEC_SEG_BOUNDARY = 1
[ 49.848000] NEW SEGMENT sg = 00000000bbdd5008!!!
[ 49.848000] __blk_segment_map_sg: length = 20480, nbytes = 4096, sum = 24576 > 65536
[ 49.848000] __blk_segment_map_sg: BIOVEC_PHYS_MERGEABLE = 0, BIOVEC_SEG_BOUNDARY = 1
[ 49.848000] NEW SEGMENT sg = 00000000bbdd5008!!!
[ 49.848000] __blk_segment_map_sg: length = 4096, nbytes = 4096, sum = 8192 > 65536
[ 49.848000] __blk_segment_map_sg: BIOVEC_PHYS_MERGEABLE = 0, BIOVEC_SEG_BOUNDARY = 1
[ 49.848000] timer_interrupt(CPU 0): delayed! cycles 2D6DC985 rem 2B2FBB next/now 19218A269E/19215EF6E3
[ 50.980000] ------------[ cut here ]------------
[ 51.036000] kernel BUG at /build/linux-4.4/linux-4.4.2/include/linux/scatterlist.h:92!
[ 51.128000] CPU: 0 PID: 62 Comm: systemd-udevd Not tainted 4.4.0-1-parisc64-smp #6 Debian 4.4.2-2
[ 51.236000] task: 00000000bbd49508 ti: 00000000bbdd4000 task.ti: 00000000bbdd4000
[ 51.324000]
[ 51.344000] YZrvWESTHLNXBCVMcbcbcbcbOGFRQPDI
[ 51.400000] PSW: 00001000000001001111110100001110 Not tainted
[ 51.468000] r00-03 000000ff0804fd0e 00000000bbdd5000 00000000404f23f8 00000000bbdd5000
[ 51.564000] r04-07 00000000409b3b10 0000000000006000 0000000000001000 0000000000000180
[ 51.660000] r08-11 0000000000000000 00000000bfdab0f0 0000000000000018 0000000000000000
[ 51.756000] r12-15 0000000000000004 00000000bbe22e00 000000007faf3188 0000000000000000
[ 51.852000] r16-19 0000000042004140 0000000000001000 0000000000000001 0000000087654321
[ 51.948000] r20-23 000000020000c18c ffffffff87654000 00000000000002a9 00000000000002ee
[ 52.044000] r24-27 0000000000000000 ffffffff87654000 00000000bbe22e80 00000000409b3b10
[ 52.140000] r28-31 00000000bbe22e80 00000000bbdd5140 00000000bbdd5170 0000c18c0000c18c
[ 52.236000] sr00-03 0000000000013800 0000000000000000 0000000000000000 0000000000011800
[ 52.332000] sr04-07 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 52.428000]
[ 52.448000] IASQ: 0000000000000000 0000000000000000 IAOQ: 00000000404f2664 00000000404f2668
[ 52.548000] IIR: 03ffe01f ISR: 0000000000000000 IOR: 000000000000005c
[ 52.628000] CPU: 0 CR30: 00000000bbdd4000 CR31: 00000000d20345e0
[ 52.712000] ORIG_R28: 0000000040b60718
[ 52.756000] IAOQ[0]: blk_rq_map_sg+0x6bc/0x7d0
[ 52.812000] IAOQ[1]: blk_rq_map_sg+0x6c0/0x7d0
[ 52.864000] RP(r2): blk_rq_map_sg+0x450/0x7d0
[ 52.920000] Backtrace:
[ 52.948000] [<00000000003f5ebc>] scsi_init_sgtable+0x94/0x1b0 [scsi_mod]
[ 53.028000] [<00000000003f6044>] scsi_init_io+0x6c/0x258 [scsi_mod]
[ 53.104000] [<000000000080e078>] sd_init_command+0x70/0xec8 [sd_mod]
[ 53.180000] scsi_init_sgtable: nr_phys_segments = 1
[ 53.180000] scsi_init_sgtable: count = 1, nents = 1
[ 53.300000]
[ 53.316000] CPU: 0 PID: 62 Comm: systemd-udevd Not tainted 4.4.0-1-parisc64-smp #6 Debian 4.4.2-2
[ 53.424000] Backtrace:
[ 53.452000] [<0000000040215bd8>] show_stack+0x20/0x38
[ 53.512000] [<0000000040520a24>] dump_stack+0x9c/0x110
[ 53.576000] [<0000000040215dac>] die_if_kernel+0x19c/0x2e0
[ 53.640000] [<0000000040216c88>] handle_interruption+0x9a8/0x9d0
[ 53.716000]
[ 53.732000] ---[ end trace 596bfe57ff9ccda5 ]---
[ 53.788000] scsi_init_sgtable: nr_phys_segments = 1
[ 53.788000] scsi_init_sgtable: count = 1, nents = 1
Helge
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