[PATCH] md: return 0 instead of error in rdev_attr_show()

[Michael Wang <yun.wang@profitbricks.com>]

sysfs_kf_read() expect the show() callback return the dumped
length, while rdev_attr_show() can return the error which lead
into overflow:

 BUG: unable to handle kernel paging request at ffff88040b084000
 IP: [<ffffffff812fe8f4>] __memmove+0x24/0x1a0
 PGD 1edb067 PUD 1ede067 PMD 406b9a063 PTE 800000040b084161
 Oops: 0003 [#1] SMP 
 [snip]
 Call Trace:
  [<ffffffff81208c30>] ? sysfs_kf_read+0x80/0xb0
  [<ffffffff81207e0b>] kernfs_fop_read+0xab/0x160
  [<ffffffff81190be8>] __vfs_read+0x28/0xd0
  [<ffffffff811911f6>] vfs_read+0x86/0x130
  [<ffffffff81191fa6>] SyS_read+0x46/0xa0
  [<ffffffff8158bc97>] entry_SYSCALL_64_fastpath+0x12/0x6a

Simply return 0 in case of error solved the problem.

Signed-off-by: Michael Wang <yun.wang@profitbricks.com>
---
 drivers/md/md.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 1db88d7..d46d714 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -3271,10 +3271,9 @@ rdev_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
 	struct rdev_sysfs_entry *entry = container_of(attr, struct rdev_sysfs_entry, attr);
 	struct md_rdev *rdev = container_of(kobj, struct md_rdev, kobj);
 
-	if (!entry->show)
-		return -EIO;
-	if (!rdev->mddev)
-		return -EBUSY;
+	if (!entry->show || !rdev->mddev)
+		return 0;
+
 	return entry->show(rdev, page);
 }
 
-- 
2.5.0