On Sunday 10 February 2008, James Bottomley wrote:
> On Sun, 2008-02-10 at 14:38 +0100, Bartlomiej Zolnierkiewicz wrote:
> > On Sunday 10 February 2008, Christoph Hellwig wrote:
> > > On Sun, Feb 10, 2008 at 12:06:10AM +0100, Bartlomiej Zolnierkiewicz wrote:
> > > > > >Please try booting with "hdx=noflush" kernel parameter or please try
> > > > > >the attached patch which should fix the issue (if my theory is correct).
> > >
> > > "hda=noflush hdb=noflush hdd=noflush" fixes the qemu setup for me.
> >
> > Thanks for testing.
> >
> > > > Thanks, I see now that there can be > 1 flush request queued at a given time.
> > > >
> > > > Please dump the old patch and try this one.
> > > >
> > > > [ Christoph: this may also fix your qemu/kvm+xfs problem. ]
> > >
> > > It doesn't hang anymore but gives me the following oops instead (that is
> > > after fixing the build as the bigger request->cmd breaks the scsi
> > > build):
> >
> > [...]
> >
> > The OOPS is most likely (again) my fault - I was rushing out to push out
> > the fix and memset() line didn't get converted.
> >
> > I prepared the new patch, documented it and started looking into SCSI
> > build breakage... and I no longer feel comfortable with the hack :(
> >
> > It seems that fixing IDE properly will be easier than auditing the whole
> > SCSI for all the weird assumptions on rq->cmd[] size (James?) so I'm back
> > to the code, in the meantime here's the updated patch:
>
> Doing something like this would have to be audited in SCSI ... we do
> assume sizeof(rq->cmd) == sizeof(scmd->cmnd) which will no longer be
> true. As long as sizeof(rq->cmd) is never used in SCSI code, it's
> probably safe.
>
> Although raising MAX_CDB by a factor of three has memory concerns as
> well, which aren't trivial and make this a bit too much of a hack. It's
> also incredibly fragile given that either ide_task_t could increase in
> size or someone could reduce MAX_CDB both with fatal consequences.
>
> Why not just use kmalloc(GFP_ATOMIC) instead? That will succeed 99% of
> the time and you can turn barriers off in a failure case. You'll have
It seems to be too late to turn barriers off as all of the above happens
_inside_ prepare_flush_fn function. Nevertheless this is a much nicer
workaround and it should be sufficent for the time being - thanks James!
> to free it in ide_end_drive_cmd(), but I think you've got (just) a spare
> tf_flag to mark a volatile task that needs kfree here.
My precious last tf_flag... fortunately some other ones can be recycled...
Sebastian/Christoph, please test the final patch (after your ACK I'll push
it to Linus together with the rest of pending IDE fixes).
From: Bartlomiej Zolnierkiewicz <bzolnier@xxxxxxxxx>
Subject: [PATCH] ide-disk: fix flush requests (take 2)
commit 813a0eb233ee67d7166241a8b389b6a76f2247f9
Author: Bartlomiej Zolnierkiewicz <bzolnier@xxxxxxxxx>
Date: Fri Jan 25 22:17:10 2008 +0100
ide: switch idedisk_prepare_flush() to use REQ_TYPE_ATA_TASKFILE requests
...
broke flush requests.
Allocating IDE command structure on the stack for flush requests is not
a very brilliant idea:
- idedisk_prepare_flush() only prepares the request and it doesn't wait
for it to be completed
- there are can be multiple flush requests queued in the queue
Fix the problem (per hints from James Bottomley) by:
- dynamically allocating ide_task_t instance using kmalloc(..., GFP_ATOMIC)
- adding new taskfile flag (IDE_TFLAG_DYN)
- calling kfree() in ide_end_drive_command() if IDE_TFLAG_DYN is set
(while at it rename 'args' to 'task' and fix whitespace damage)
[ This will be fixed properly before 2.6.25 but this bug is rather
critical and the proper solution requires some more work + testing. ]
Thanks to Sebastian Siewior and Christoph Hellwig for reporitng the
problem and testing patches (extra thanks to Sebastian for bisecting
it to the guilty commmit).
Cc: Sebastian Siewior <ide-bug@xxxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Cc: Jens Axboe <jens.axboe@xxxxxxxxxx>
Cc: Tejun Heo <htejun@xxxxxxxxx>
Cc: Sergei Shtylyov <sshtylyov@xxxxxxxxxxxxx>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@xxxxxxxxx>
---
drivers/ide/ide-disk.c | 18 +++++++++++-------
drivers/ide/ide-io.c | 16 ++++++++++------
include/linux/ide.h | 2 ++
3 files changed, 23 insertions(+), 13 deletions(-)
Index: b/drivers/ide/ide-disk.c
===================================================================
--- a/drivers/ide/ide-disk.c
+++ b/drivers/ide/ide-disk.c
@@ -590,20 +590,24 @@ static ide_proc_entry_t idedisk_proc[] =
static void idedisk_prepare_flush(struct request_queue *q, struct request *rq)
{
ide_drive_t *drive = q->queuedata;
- ide_task_t task;
+ ide_task_t *task = kmalloc(sizeof(*task), GFP_ATOMIC);
- memset(&task, 0, sizeof(task));
+ /* FIXME: map struct ide_taskfile on rq->cmd[] */
+ BUG_ON(task == NULL);
+
+ memset(task, 0, sizeof(*task));
if (ide_id_has_flush_cache_ext(drive->id) &&
(drive->capacity64 >= (1UL << 28)))
- task.tf.command = WIN_FLUSH_CACHE_EXT;
+ task->tf.command = WIN_FLUSH_CACHE_EXT;
else
- task.tf.command = WIN_FLUSH_CACHE;
- task.tf_flags = IDE_TFLAG_OUT_TF | IDE_TFLAG_OUT_DEVICE;
- task.data_phase = TASKFILE_NO_DATA;
+ task->tf.command = WIN_FLUSH_CACHE;
+ task->tf_flags = IDE_TFLAG_OUT_TF | IDE_TFLAG_OUT_DEVICE |
+ IDE_TFLAG_DYN;
+ task->data_phase = TASKFILE_NO_DATA;
rq->cmd_type = REQ_TYPE_ATA_TASKFILE;
rq->cmd_flags |= REQ_SOFTBARRIER;
- rq->special = &task;
+ rq->special = task;
}
/*
Index: b/drivers/ide/ide-io.c
===================================================================
--- a/drivers/ide/ide-io.c
+++ b/drivers/ide/ide-io.c
@@ -361,17 +361,21 @@ void ide_end_drive_cmd (ide_drive_t *dri
spin_unlock_irqrestore(&ide_lock, flags);
if (rq->cmd_type == REQ_TYPE_ATA_TASKFILE) {
- ide_task_t *args = (ide_task_t *) rq->special;
+ ide_task_t *task = (ide_task_t *)rq->special;
+
if (rq->errors == 0)
- rq->errors = !OK_STAT(stat,READY_STAT,BAD_STAT);
-
- if (args) {
- struct ide_taskfile *tf = &args->tf;
+ rq->errors = !OK_STAT(stat, READY_STAT, BAD_STAT);
+
+ if (task) {
+ struct ide_taskfile *tf = &task->tf;
tf->error = err;
tf->status = stat;
- ide_tf_read(drive, args);
+ ide_tf_read(drive, task);
+
+ if (task->tf_flags & IDE_TFLAG_DYN)
+ kfree(task);
}
} else if (blk_pm_request(rq)) {
struct request_pm_state *pm = rq->data;
Index: b/include/linux/ide.h
===================================================================
--- a/include/linux/ide.h
+++ b/include/linux/ide.h
@@ -906,6 +906,8 @@ enum {
IDE_TFLAG_IN_DEVICE,
/* force 16-bit I/O operations */
IDE_TFLAG_IO_16BIT = (1 << 30),
+ /* ide_task_t was allocated using kmalloc() */
+ IDE_TFLAG_DYN = (1 << 31),
};
struct ide_taskfile {
-
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