On Tue, 14 Jan 2014, Kent Overstreet wrote:
>
> Does the below patch look like what we want? I'm assuming that if
You don't fill me with confidence ;)
> multiple WRITE_SAME bios are merged, since they're all writing the same
> data we can consider the entire request to be a single segment.
>
> commit 1755e7ffc5745591d37b8956ce2512f4052a104a
> Author: Kent Overstreet <k...@daterainc.com>
> Date: Tue Jan 14 14:22:01 2014 -0800
>
> block: Explicitly handle discard/write same when counting segments
>
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 8f8adaa..7d977f8 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -21,6 +21,12 @@ static unsigned int __blk_recalc_rq_segments(struct
> request_queue *q,
> if (!bio)
> return 0;
>
> + if (bio->bi_rw & REQ_DISCARD)
> + return 0;
> +
> + if (bio->bi_rw & REQ_WRITE_SAME)
> + return 1;
> +
> fbio = bio;
> cluster = blk_queue_cluster(q);
> seg_size = 0;
For me this just shifts the crash,
from __blk_recalc_rq_segments() to blk_rq_map_sg():
blk_rq_map_sg
scsi_init_sgtable
scsi_init_io
scsi_setup_blk_pc_cmnd
sd_prep_fn
blk_peek_request
scsi_request_fn
__blk_run_queue
blk_run_queue
scsi_run_queue
scsi_next_command
scsi_io_completion
scsi_finish_command
scsi_softirq_done
blk_done_softirq
__do_softirq
irq_exit
do_IRQ
common_interrupt
<EOI>
cpuidle_idle_call
arch_cpu_idle
cpu_startup_entry
start_secondary
It's GPF'ing on struct scatter_list *sg 0x800000001473e064 in
static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
{
unsigned long page_link = sg->page_link & 0x3;
It appears to be in the static inline __blk_segment_map_sg(),
and that GPF'ing address is what it just got from sg_next().
Sorry, this isn't the kind of dump you'll be used to, but it's the
best I can do at the moment, and I've just had to reboot the machine.
O, tried again and it hit the BUG_ON(count > sdb->table.nents)
on line 1048 of drivers/scsi/scsi_lib.c:
scsi_init_sgtable
<IRQ> scsi_init_io
scsi_setup_blk_pc_cmnd
sd_setup_discard_cmnd
sd_prep_fn
blk_peek_request
etc. as before
I'll have to leave the machine shortly - I'm rather hoping
you can do your own discard testing to see such crashes.
Thanks,
Hugh
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