linux-kernel - Re: [PATCH] IDE: Fix HDIO_DRIVE

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Message-Id: <200806240041.42796.bzolnier@gmail.com>
Date:	Tue, 24 Jun 2008 00:41:42 +0200
From:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
To:	Elias Oltmanns <eo@...ensachen.de>
Cc:	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
	Randy Dunlap <randy.dunlap@...cle.com>
Subject: Re: [PATCH] IDE: Fix HDIO_DRIVE_RESET handling

On Monday 23 June 2008, Elias Oltmanns wrote:
> Bartlomiej Zolnierkiewicz <bzolnier@...il.com> wrote:
> > Hi,
> >
> > On Thursday 19 June 2008, Elias Oltmanns wrote:
> >> Hi Bart,
> >> 
> >> currently, the code path executing an HDIO_DRIVE_RESET ioctl is broken
> >> in various ways.  Firstly, ide_abort() is called with the ide_lock held
> >> and may call ide_end_request() further down the line which will try to
> >> grab the same lock again.  More importantly though, the whole concept of
> >> aborting an inflight request is flawed -- at least as far as ide_abort()
> >> is concerned.
> >> 
> >> The patch below tries to address these issues by handling the
> >> HDIO_DRIVE_RESET ioctl in-band.
> [...]
> > One more thing, ide-2.6 is for syncing with Linus _only_ (it seems I'm to
> > blame for the confusion), please rebase your work on top of pata-2.6 quilt
> > tree (some comments which should ease the transition below):
> >
> > 	http://kernel.org/pub/linux/kernel/people/bart/pata-2.6/
> >
> > [ This tree is pulled into linux-next so you may prefer to just use the
> >   latest -next snapshost instead. ]
> 
> Indeed, the following patch series is based on nex-20080620.  Just to be
> absolutely clear though, this is actually a bug fix since a
> 
> # hdparm -w /dev/hda
> 
> currently freezes the system if there happens to be any I/O operation in
> progress.  Not sure whether this is serious enough for -rc or, indeed,
> -stable trees, but I thought I'd mention it.

According to 'man hdparm':

       -w     Perform a device reset (DANGEROUS).  Do NOT use this option.  It
              exists for unlikely situations where a reboot might otherwise be
              required to get a confused drive back into a useable state.

so I don't think that a rush is necessary (however we may still want to get
patch #1 in for 2.6.26).

BTW Your fix adds framework which can be re-used for fixing locking of IDE
settings (+ it finally makes sense to dust-off my IDE settings rework which
was always low-prio and was never posted :) and maybe it could be also used
for drive->special handling.

> [...]
> >> +	rq->cmd[0] = REQ_DRIVE_RESET;
> >> +	rq->cmd_type = REQ_TYPE_SPECIAL;
> >> +	rq->cmd_flags |= REQ_SOFTBARRIER;
> >> +	ide_do_drive_cmd(drive, rq, ide_end);
> >
> > ide_do_drive_cmd() now handles only ide_preempt + it seems that previously
> > the ioctl would wait till the reset is complete so probably this needs to
> > use blk_execute_rq() instead
> 
> There is some uncertainty here: Previously, the code didn't actually
> wait for the reset to complete before returning but did so right after
> the reset sequence had been initiated.  It might be desirable to wait
> for completion before returning though and that's the way I've
> implemented it in the new patch (first in the series).  This has the
> advantage that user space could be informed when anything should have
> gone wrong (like a timeout).  This would obviously mean a functional
> change visible from user space but then fixing the bug in the first
> place is a change visible in user space.  See the fourth patch in the
> series for what I've had in mind.
> 
> >
> > [...]
> >
> > Oh, and now that you've fixed HDIO_DRIVE_RESET you get the following bonus:
> > ide_abort(), __ide_abort() and ide_driver_t.abort all can be removed in the
> > incremental patch! ;)
> 
> Done.  It's the second in the series.

Thanks.

> So here is the summary of the patch series to come:
> 
> 1. Fixes the buggy implementation of HDIO_DRIVE_RESET handling.

Two minor issues here (see reply to the patch).

> 2. Removes all code that has been made superfluous by the previous
>    change.
> 3. Documents the way HDIO_DRIVE_RESET is handled accurately.
> 4. Adds some more error reporting facilities and documents them as well.
> 
> Please be particularly alert when reviewing the last patch.  I merely
> did what seemed to be the right and obvious thing to do but I ironed out
> some irregularities along the way which (for all improbability) may have
> been there for some reason or other.  It beats me, for instance, why
> ->polling but not ->resetting should be reset to 0 when
> sil_sata_reset_poll() returns non zero.  So, I now both are 0 once any
> of the poll functions returns ide_stopped.

Looks OK but please move the above description to the patch description.

Patches #2 and #3 also look good.

Bart
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