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Re: block: flush queued bios when the process blocks

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On Tue, Oct 06 2015 at  9:28am -0400,
Mikulas Patocka <mpatocka@redhat.com> wrote:

> 
> 
> On Mon, 5 Oct 2015, Mike Snitzer wrote:
> 
> > Mikulas,
> > 
> > Could it be that cond_resched() wasn't unplugging?  As was
> > recently raised in this thread: https://lkml.org/lkml/2015/9/18/378
> > Chris Mason's patch from that thread fixed this	issue... I _think_ Linus
> > has since committed Chris' work but I haven't kept my finger on the
> > pulse of that issue.
> 
> I think it doesn't matter (regarding correctness) if cond_reched unplugs 
> on not. If it didn't unplug, the process will be scheduled later, and it 
> will eventually reach the point where it unplugs.

Couldn't the original deadlock you fixed (as described in your first
patch) manifest when a new process is scheduled?
 
> > FYI, I've put rebased versions of your 2 patches in my wip branch, see:
> > http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/log/?h=wip
> > 
> > I tweaked the 2nd patch that adds bio_list to plug so that
> > generic_make_request's checks for in_generic_make_request isn't racey
> > (your original patch could happen to have current-plug set but
> > in_generic_make_request not yet set).
> 
> I don't recommend that second patch 
> (http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/commit/?h=wip&id=5e740c2e45a767d8d6ef8ca36b0db705ef6259c4). 
> The patch just complicates things without adding any value. It's also not 
> correct because it plugs bios at places when bios aren't supposed to be 
> plugged

Avoiding another hook the the scheduler is a requirement (from Jens).
"without adding any value": it offers a different strategy for recording
bios to the bio_list by making it part of the plug.  The plug doesn't
actually block bios like requests are plugged.  What am I missing?
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Thread

Re: block: flush queued bios when the process blocks Mike Snitzer <snitzer@redhat.com> - 2015-10-05 23:00 +0200
  Re: block: flush queued bios when the process blocks Mikulas Patocka <mpatocka@redhat.com> - 2015-10-06 15:30 +0200
    Re: block: flush queued bios when the process blocks Mike Snitzer <snitzer@redhat.com> - 2015-10-06 15:50 +0200
      Re: block: flush queued bios when the process blocks Mikulas Patocka <mpatocka@redhat.com> - 2015-10-06 16:20 +0200
      Re: block: flush queued bios when the process blocks Mikulas Patocka <mpatocka@redhat.com> - 2015-10-06 16:30 +0200
  Re: [dm-devel] block: flush queued bios when the process blocks Mikulas Patocka <mpatocka@redhat.com> - 2015-10-06 20:20 +0200
    Re: block: flush queued bios when the process blocks Mike Snitzer <snitzer@redhat.com> - 2015-10-06 21:00 +0200
      [PATCH v2] block: flush queued bios when the process blocks Mike Snitzer <snitzer@redhat.com> - 2015-10-06 22:20 +0200
        Re: [PATCH v2] block: flush queued bios when the process blocks Mike Snitzer <snitzer@redhat.com> - 2015-10-06 22:30 +0200
        Re: [PATCH v2] block: flush queued bios when the process blocks Mikulas Patocka <mpatocka@redhat.com> - 2015-10-08 17:10 +0200
          Re: [PATCH v2] block: flush queued bios when the process blocks Mike Snitzer <snitzer@redhat.com> - 2015-10-08 17:10 +0200
            Re: [PATCH v2] block: flush queued bios when the process blocks Mike Snitzer <snitzer@redhat.com> - 2015-10-09 22:00 +0200
              Re: [PATCH v2] block: flush queued bios when the process blocks Mike Snitzer <snitzer@redhat.com> - 2015-10-09 22:00 +0200
                [PATCH v3 for-4.4] block: flush queued bios when process blocks to  avoid deadlock Mike Snitzer <snitzer@redhat.com> - 2015-10-14 22:50 +0200
                Re: [PATCH v3 for-4.4] block: flush queued bios when process blocks to avoid deadlock Jeff Moyer <jmoyer@redhat.com> - 2015-10-14 23:50 +0200
                Re: [PATCH v3 for-4.4] block: flush queued bios when process blocks  to avoid deadlock Ming Lei <tom.leiming@gmail.com> - 2015-10-17 18:10 +0200
              Re: [PATCH v2] block: flush queued bios when the process blocks Ming Lei <tom.leiming@gmail.com> - 2015-10-15 05:30 +0200
                Re: [PATCH v2] block: flush queued bios when the process blocks Mike Snitzer <snitzer@redhat.com> - 2015-10-15 10:10 +0200
                Re: [PATCH v2] block: flush queued bios when the process blocks Ming Lei <tom.leiming@gmail.com> - 2015-10-16 05:10 +0200
                Re: [PATCH v2] block: flush queued bios when the process blocks Mike Snitzer <snitzer@redhat.com> - 2015-10-16 17:30 +0200
                Re: [PATCH v2] block: flush queued bios when the process blocks Ming Lei <tom.leiming@gmail.com> - 2015-10-17 18:00 +0200
        Re: [PATCH v2] block: flush queued bios when the process blocks kbuild test robot <lkp@intel.com> - 2015-10-09 14:00 +0200

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