diff for duplicates of <6db16aa3a7c56b6dcca2d10b4e100a780c740081.camel@wdc.com>

diff --git a/a/1.txt b/N1/1.txt
index 7f158f5..f5ee908 100644
--- a/a/1.txt
+++ b/N1/1.txt
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\ No newline at end of file
+On Wed, 2018-05-16 at 17:16 +0200, Dmitry Vyukov wrote:
+> On Wed, May 16, 2018 at 4:56 PM, Bart Van Assche <Bart.VanAssche@wdc.com> wrote:
+> > On Wed, 2018-05-16 at 22:05 +0900, Tetsuo Handa wrote:
+> > > diff --git a/block/blk-core.c b/block/blk-core.c
+> > > index 85909b4..59e2496 100644
+> > > --- a/block/blk-core.c
+> > > +++ b/block/blk-core.c
+> > > @@ -951,10 +951,10 @@ int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)
+> > >               smp_rmb();
+> > > 
+> > >               wait_event(q->mq_freeze_wq,
+> > > -                        (atomic_read(&q->mq_freeze_depth) == 0 &&
+> > > -                         (preempt || !blk_queue_preempt_only(q))) ||
+> > > +                        atomic_read(&q->mq_freeze_depth) ||
+> > > +                        (preempt || !blk_queue_preempt_only(q)) ||
+> > >                          blk_queue_dying(q));
+> > > -             if (blk_queue_dying(q))
+> > > +             if (atomic_read(&q->mq_freeze_depth) || blk_queue_dying(q))
+> > >                       return -ENODEV;
+> > >       }
+> > >  }
+> > 
+> > That change looks wrong to me.
+> 
+> Hi Bart,
+> 
+> Why does it look wrong to you?
+
+Because that change conflicts with the purpose of queue freezing and also because
+that change would inject I/O errors in code paths that shouldn't inject I/O errors.
+Please have a look at e.g. generic_make_request(). From the start of that function:
+
+	if (blk_queue_enter(q, flags) < 0) {
+		if (!blk_queue_dying(q) && (bio->bi_opf & REQ_NOWAIT))
+			bio_wouldblock_error(bio);
+		else
+			bio_io_error(bio);
+		return ret;
+	}
+
+The above patch changes the behavior of blk_queue_enter() code from waiting while
+q->mq_freeze_depth != 0 into returning -ENODEV while the request queue is frozen.
+That will cause generic_make_request() to call bio_io_error(bio) while a request
+queue is frozen if REQ_NOWAIT has not been set, which is the default behavior. So
+any operation that freezes the queue temporarily, e.g. changing the queue depth,
+concurrently with I/O processing can cause I/O to fail with -ENODEV. As you
+probably know failure of write requests has very annoying consequences. It e.g.
+causes filesystems to go into read-only mode. That's why I think that the above
+change is completely wrong.
+
+Bart.
\ No newline at end of file
diff --git a/a/content_digest b/N1/content_digest
index b82c8fc..cec4dbc 100644
--- a/a/content_digest
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+  "On Wed, 2018-05-16 at 17:16 +0200, Dmitry Vyukov wrote:\n",
+  "> On Wed, May 16, 2018 at 4:56 PM, Bart Van Assche <Bart.VanAssche\@wdc.com> wrote:\n",
+  "> > On Wed, 2018-05-16 at 22:05 +0900, Tetsuo Handa wrote:\n",
+  "> > > diff --git a/block/blk-core.c b/block/blk-core.c\n",
+  "> > > index 85909b4..59e2496 100644\n",
+  "> > > --- a/block/blk-core.c\n",
+  "> > > +++ b/block/blk-core.c\n",
+  "> > > \@\@ -951,10 +951,10 \@\@ int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)\n",
+  "> > >               smp_rmb();\n",
+  "> > > \n",
+  "> > >               wait_event(q->mq_freeze_wq,\n",
+  "> > > -                        (atomic_read(&q->mq_freeze_depth) == 0 &&\n",
+  "> > > -                         (preempt || !blk_queue_preempt_only(q))) ||\n",
+  "> > > +                        atomic_read(&q->mq_freeze_depth) ||\n",
+  "> > > +                        (preempt || !blk_queue_preempt_only(q)) ||\n",
+  "> > >                          blk_queue_dying(q));\n",
+  "> > > -             if (blk_queue_dying(q))\n",
+  "> > > +             if (atomic_read(&q->mq_freeze_depth) || blk_queue_dying(q))\n",
+  "> > >                       return -ENODEV;\n",
+  "> > >       }\n",
+  "> > >  }\n",
+  "> > \n",
+  "> > That change looks wrong to me.\n",
+  "> \n",
+  "> Hi Bart,\n",
+  "> \n",
+  "> Why does it look wrong to you?\n",
+  "\n",
+  "Because that change conflicts with the purpose of queue freezing and also because\n",
+  "that change would inject I/O errors in code paths that shouldn't inject I/O errors.\n",
+  "Please have a look at e.g. generic_make_request(). From the start of that function:\n",
+  "\n",
+  "\tif (blk_queue_enter(q, flags) < 0) {\n",
+  "\t\tif (!blk_queue_dying(q) && (bio->bi_opf & REQ_NOWAIT))\n",
+  "\t\t\tbio_wouldblock_error(bio);\n",
+  "\t\telse\n",
+  "\t\t\tbio_io_error(bio);\n",
+  "\t\treturn ret;\n",
+  "\t}\n",
+  "\n",
+  "The above patch changes the behavior of blk_queue_enter() code from waiting while\n",
+  "q->mq_freeze_depth != 0 into returning -ENODEV while the request queue is frozen.\n",
+  "That will cause generic_make_request() to call bio_io_error(bio) while a request\n",
+  "queue is frozen if REQ_NOWAIT has not been set, which is the default behavior. So\n",
+  "any operation that freezes the queue temporarily, e.g. changing the queue depth,\n",
+  "concurrently with I/O processing can cause I/O to fail with -ENODEV. As you\n",
+  "probably know failure of write requests has very annoying consequences. It e.g.\n",
+  "causes filesystems to go into read-only mode. That's why I think that the above\n",
+  "change is completely wrong.\n",
+  "\n",
+  "Bart."
 ]
 
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