>>> "Joe Jin" <joe.jin@xxxxxxxxxx> 20.01.10 03:06 >>>
>sysfs did not provide lock to handle this, not sure if developer
>think it is not necessary or they'd like to caller to handled it.
A lock is probably not the usual way to deal with this; ref-counting
would seem more common. Nevertheless I think adding a lock will
take care of the issue here.
>--- a/drivers/xen/blktap/xenbus.c Fri Jan 08 13:07:17 2010 +0000
>+++ b/drivers/xen/blktap/xenbus.c Wed Jan 20 10:00:53 2010 +0800
>...
>@@ -122,10 +123,15 @@
> struct device_attribute *attr, \
> char *buf) \
> { \
>+ ssize_t ret = -ENODEV; \
> struct xenbus_device *dev = to_xenbus_device(_dev); \
The use of to_xenbus_device() here makes ...
>- struct backend_info *be = dev->dev.driver_data; \
>+ struct backend_info *be; \
> \
>- return sprintf(buf, format, ##args); \
>+ read_lock(&sysfs_read_lock); \
>+ if (dev && (be = dev->dev.driver_data) && be->blkif) \
... the checking of dev here useless (and the blkback part of the patch
doesn't do the same).
>+ ret = sprintf(buf, format, ##args); \
>+ read_unlock(&sysfs_read_lock); \
>+ return ret; \
> } \
> static DEVICE_ATTR(name, S_IRUGO, show_##name, NULL)
>
And btw., in both cases with the lock added there's no need to check
both 'be' and 'be->blkif', since be->blkif can't be NULL when be is
non-NULL.
Jan
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