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Date: Wed, 24 Jul 2002 14:50:37 +0200
From: Jens Axboe <axboe@suse.de>
To: Bartlomiej Zolnierkiewicz <B.Zolnierkiewicz@elka.pw.edu.pl>
Cc: martin@dalecki.de, linux-kernel@vger.kernel.org
Subject: Re: please DON'T run 2.5.27 with IDE!
Message-ID: <20020724125037.GB15201@suse.de>
References: <20020724124124.GA15201@suse.de> <Pine.SOL.4.30.0207241446130.15605-100000@mion.elka.pw.edu.pl>
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On Wed, Jul 24 2002, Bartlomiej Zolnierkiewicz wrote:
> 
> On Wed, 24 Jul 2002, Jens Axboe wrote:
> 
> > On Wed, Jul 24 2002, Bartlomiej Zolnierkiewicz wrote:
> > > > void blk_start_queue(request_queue_t *q)
> > > > {
> > > >          if (test_bit(QUEUE_FLAG_STOPPED, &q->queue_flags)) {
> > > >                  unsigned long flags;
> > > >
> > > > ================== possigle race here for qeue_flags BTW.
> > > >
> > > >                  spin_lock_irqsave(q->queue_lock, flags);
> > > >                  clear_bit(QUEUE_FLAG_STOPPED, &q->queue_flags);
> > > >
> > > >                  if (!elv_queue_empty(q))
> > > >                          q->request_fn(q);
> > > > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > > > If we call it from within request_fn then if this isn't recursion on the
> > > > kernel stack then I don't know...
> > >
> > > You really don't know.
> > >
> > > And funny thing is I have diffirent blk_start_queue() function in my tree
> > > (2.5.27) ? Without described above race and without possibilty of
> > > recursion...
> > >
> > > 2.5.27:drivers/block/ll_rw_blk.c
> > > void blk_start_queue(request_queue_t *q)
> > > {
> > >         if (test_and_clear_bit(QUEUE_FLAG_STOPPED, &q->queue_flags)) {
> > >                 unsigned long flags;
> > >
> > >                 spin_lock_irqsave(q->queue_lock, flags);
> > >                 if (!elv_queue_empty(q))
> > >                         q->request_fn(q);
> > >                 spin_unlock_irqrestore(q->queue_lock, flags);
> > >         }
> > > }
> >
> > Yep, the version Martin posted must be really old.
> 
> It's worst. Martin's version exists only in his tree (mind?).

:-)

> I checked back revision and blk_start_queue() was inroduced in 2.5.19
> and it was the correct one.

There were buggy versions at one point, however they may not have made it
into a full release. In that case it was just bk version of 2.5.19-pre
effectively. I forget the details :-)

-- 
Jens Axboe

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