[PATCH] Fix soft lockup with iSeries viocd driver

[PATCH] Fix soft lockup with iSeries viocd driver

[Tony Breeds]

From: Tony Breeds <tony@bakeyournoodle.com>

Fix soft lockup with iSeries viocd driver, caused by eventually calling
end_that_request_first() with nr_bytes 0.

The lockup is triggered by hald, interrogating the device.

Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

---
 viocd.c |   27 +++++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

Index: linux-2.6.20-rc5/drivers/cdrom/viocd.c
===================================================================
--- linux-2.6.20-rc5.orig/drivers/cdrom/viocd.c
+++ linux-2.6.20-rc5/drivers/cdrom/viocd.c
@@ -376,6 +376,25 @@ static int send_request(struct request *
        return 0;
 }
 
+static void viocd_end_request(struct request *req, int uptodate)
+{
+       int nsectors = req->hard_nr_sectors;
+
+       /*
+        * Make sure it's fully ended, and ensure that we process
+        * at least one sector.
+        */
+       if (blk_pc_request(req))
+               nsectors = (req->data_len + 511) >> 9;
+       if (!nsectors)
+               nsectors = 1;
+
+       if (end_that_request_first(req, uptodate, nsectors))
+               BUG();
+       add_disk_randomness(req->rq_disk);
+       blkdev_dequeue_request(req);
+       end_that_request_last(req, uptodate);
+}
 
 static int rwreq;
 
@@ -385,11 +404,11 @@ static void do_viocd_request(request_que
 
        while ((rwreq == 0) && ((req = elv_next_request(q)) != NULL)) {
                if (!blk_fs_request(req))
-                       end_request(req, 0);
+                       viocd_end_request(req, 0);
                else if (send_request(req) < 0) {
                        printk(VIOCD_KERN_WARNING
                                        "unable to send message to OS/400!");
-                       end_request(req, 0);
+                       viocd_end_request(req, 0);
                } else
                        rwreq++;
        }
@@ -601,9 +620,9 @@ return_complete:
                                        "with rc %d:0x%04X: %s\n",
                                        req, event->xRc,
                                        bevent->sub_result, err->msg);
-                       end_request(req, 0);
+                       viocd_end_request(req, 0);
                } else
-                       end_request(req, 1);
+                       viocd_end_request(req, 1);
 
                /* restart handling of incoming requests */
                spin_unlock_irqrestore(&viocd_reqlock, flags);





Yours Tony

  linux.conf.au        http://linux.conf.au/ || http://lca2008.linux.org.au/
  Jan 28 - Feb 02 2008 The Australian Linux Technical Conference!



Yours Tony

  linux.conf.au        http://linux.conf.au/ || http://lca2008.linux.org.au/
  Jan 28 - Feb 02 2008 The Australian Linux Technical Conference!

Re: [PATCH] Fix soft lockup with iSeries viocd driver

[Andrew Morton]

On Thu, 1 Mar 2007 14:56:40 +1100 tony@bakeyournoodle.com (Tony Breeds) wrote:

> From: Tony Breeds <tony@bakeyournoodle.com>
> 
> Fix soft lockup with iSeries viocd driver, caused by eventually calling
> end_that_request_first() with nr_bytes 0.
> 
> The lockup is triggered by hald, interrogating the device.
> 

What causes the lockup, and how does this patch fix it?

> 
> Index: linux-2.6.20-rc5/drivers/cdrom/viocd.c
> ===================================================================
> --- linux-2.6.20-rc5.orig/drivers/cdrom/viocd.c
> +++ linux-2.6.20-rc5/drivers/cdrom/viocd.c
> @@ -376,6 +376,25 @@ static int send_request(struct request *
>         return 0;
>  }
>  
> +static void viocd_end_request(struct request *req, int uptodate)
> +{
> +       int nsectors = req->hard_nr_sectors;

Your email client replaces tabs with spaces.  I fixed this patch up.

Re: [PATCH] Fix soft lockup with iSeries viocd driver

[Stephen Rothwell]

[-- Attachment #1: Type: text/plain, Size: 999 bytes --]

On Thu, 1 Mar 2007 00:37:48 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Thu, 1 Mar 2007 14:56:40 +1100 tony@bakeyournoodle.com (Tony Breeds) wrote:
>
> > From: Tony Breeds <tony@bakeyournoodle.com>
> >
> > Fix soft lockup with iSeries viocd driver, caused by eventually calling
> > end_that_request_first() with nr_bytes 0.
> >
> > The lockup is triggered by hald, interrogating the device.
> >
>
> What causes the lockup, and how does this patch fix it?

Some versions of hald do an SG_IO ioctl on the viocd device which becomes
a request with hard_nr_sectors and hard_cur_sectors set to zero.  Passing
zero as the number of sectors to end_request() (which calls
end_that_request_first()) causes an infinite loop when the bio is being
freed.  This patch makes sure that the zero is never passed. It only
requires some number larger the the request size the terminate the loop.

--
Cheers,
Stephen Rothwell                    sfr@canb.auug.org.au
http://www.canb.auug.org.au/~sfr/

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