linux-kernel - [029/146] block: always allocate genhd->ev if check

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Date:	Wed, 01 Jun 2011 16:59:25 +0900
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Tejun Heo <tj@...nel.org>, Jens Axboe <jaxboe@...ionio.com>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: [029/146] block: always allocate genhd->ev if check_events is

2.6.38-stable review patch.  If anyone has any objections, please let us know.

------------------
 implemented

From: Tejun Heo <tj@...nel.org>

commit 75e3f3ee3c64968d42f4843ec49e579f84b5aa0c upstream.

9fd097b149 (block: unexport DISK_EVENT_MEDIA_CHANGE for legacy/fringe
drivers) removed DISK_EVENT_MEDIA_CHANGE from legacy/fringe block
drivers which have inadequate ->check_events().  Combined with earlier
change 7c88a168da (block: don't propagate unlisted DISK_EVENTs to
userland), this enables using ->check_events() for internal processing
while avoiding enabling in-kernel block event polling which can lead
to infinite event loop.

Unfortunately, this made many drivers including floppy without any bit
set in disk->events and ->async_events in which case disk_add_events()
simply skipped allocation of disk->ev, which disables whole event
handling.  As ->check_events() is still used during open processing
for revalidation, this can lead to open failure.

This patch always allocates disk->ev if ->check_events is implemented.
In the long term, it would make sense to simply include the event
structure inline into genhd as it's now used by virtually all block
devices.

Signed-off-by: Tejun Heo <tj@...nel.org>
Reported-by: Ondrej Zary <linux@...nbow-software.org>
Reported-by: Alex Villacis Lasso <avillaci@...bo.fiec.espol.edu.ec>
Signed-off-by: Jens Axboe <jaxboe@...ionio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 block/genhd.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1724,7 +1724,7 @@ static void disk_add_events(struct gendi
 {
 	struct disk_events *ev;

-	if (!disk->fops->check_events || !(disk->events | disk->async_events))
+	if (!disk->fops->check_events)
 		return;

 	ev = kzalloc(sizeof(*ev), GFP_KERNEL);

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