On 2010-01-19 10:25, Jan Beulich wrote:
> >>> "Joe Jin" <joe.jin@xxxxxxxxxx> 19.01.10 10:52 >>>
> >At backend driver blkback and blktap, when checking statistics information,
> >at the time vbd device remove, kernel will crash.
> >
> >Below patch will fix it, please review and apply.
>
> This isn't a complete fix if I follow your analysis: There's still a race
> between blk{back,tap}_remove() freeing be->blkif/be and the sysfs
> code. dev->dev.driver_data (and possibly be->blkif) must be cleared
> before freeing it (them).
>
Thanks for you point.
Anyway, I think need to add some check at VBD_SHOW even cleared
dev->dev.driver_data before free it, sysfs->fops() have been
initialized when call open(), and later when read the file, call
trace will fall VBD_SHOW defined function(s), so it should crashed.
The checks may look like below?
diff -r 6061d5615522 drivers/xen/blkback/xenbus.c
--- a/drivers/xen/blkback/xenbus.c Fri Jan 08 13:07:17 2010 +0000
+++ b/drivers/xen/blkback/xenbus.c Tue Jan 19 19:30:32 2010 +0800
@@ -104,10 +104,13 @@
struct device_attribute *attr, \
char *buf) \
{ \
+ ssize_t ret = -ENODEV; \
struct xenbus_device *dev = to_xenbus_device(_dev); \
- struct backend_info *be = dev->dev.driver_data; \
+ struct backend_info *be; \
\
- return sprintf(buf, format, ##args); \
+ if (dev && (be = dev->dev.driver_data) && be->blkif) \
+ ret = sprintf(buf, format, ##args); \
+ return ret; \
} \
static DEVICE_ATTR(name, S_IRUGO, show_##name, NULL)
diff -r 6061d5615522 drivers/xen/blktap/xenbus.c
--- a/drivers/xen/blktap/xenbus.c Fri Jan 08 13:07:17 2010 +0000
+++ b/drivers/xen/blktap/xenbus.c Tue Jan 19 19:30:32 2010 +0800
@@ -122,10 +122,13 @@
struct device_attribute *attr, \
char *buf) \
{ \
+ ssize_t ret = -ENODEV; \
struct xenbus_device *dev = to_xenbus_device(_dev); \
- struct backend_info *be = dev->dev.driver_data; \
+ struct backend_info *be; \
\
- return sprintf(buf, format, ##args); \
+ if (dev && (be = dev->dev.driver_data) && be->blkif) \
+ ret = sprintf(buf, format, ##args); \
+ return ret; \
} \
static DEVICE_ATTR(name, S_IRUGO, show_##name, NULL)
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