Re: [PATCH] Bug fix for the s390 dcssblk driver

[Gerald Schaefer <gerald.schaefer@de.ibm.com>]

On Mon, 2007-10-22 at 13:37 +0200, Cornelia Huck wrote:
> On Sun, 21 Oct 2007 23:46:49 -0400,
> emist <emistz@gmail.com> wrote:
> 
> > # This patch fixes a memory corruption bug in the s390 dcssblk driver.
> > # The bug occurs when an attempt to change the type of a segment
> > # returns an error. At this point the driver tries to remove the segment in
> > # question while some of the device's attributes are in use. This causes the
> > # driver to hang.
> 
> Hm, seems we missed another of those device attributes exhibiting
> suicidal tendencies...
> 
> Tejun has a patchset allowing device attributes to commit suicide (see
> http://marc.info/?l=linux-kernel&m=119027371416452&w=2), although I'm
> not sure what its current status is. Until then, you would need to use
> device_schedule_callback() to commit suicide.
> 
> This all of course only applies if killing the segment is better than
> leaving it in its current state, but others can make a better judgement
> on that :)

Hi,

thanks for reporting this bug, seems like we forgot to consider the
suicidal behavior of this driver when the device_unregister() stuff was
changed.

The best solution for now would be to use the scheduled callback
function, like Cornelia described. If segment_modify_shared() should
fail, the DCSS segment will be unloaded. Calling the function again
with the old "shared" flag will not help because it will not reload
the segment. So we need to remove/unregister the device in this error
path, and for now this should be done with device_schedule_callback().

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
---

 dcssblk.c |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)

Index: linux-2.6.23/drivers/s390/block/dcssblk.c
===================================================================
--- linux-2.6.23.orig/drivers/s390/block/dcssblk.c
+++ linux-2.6.23/drivers/s390/block/dcssblk.c
@@ -193,6 +193,12 @@ dcssblk_segment_warn(int rc, char* seg_n
        }
 }

+static void dcssblk_unregister_callback(struct device *dev)
+{
+       device_unregister(dev);
+       put_device(dev);
+}
+
 /*
  * device attribute for switching shared/nonshared (exclusive)
  * operation (show + store)
@@ -276,8 +282,7 @@ removeseg:
        blk_cleanup_queue(dev_info->dcssblk_queue);
        dev_info->gd->queue = NULL;
        put_disk(dev_info->gd);
-       device_unregister(dev);
-       put_device(dev);
+       rc = device_schedule_callback(dev, dcssblk_unregister_callback);
 out:
        up_write(&dcssblk_devices_sem);
        return rc;