linux-kernel - [PATCH 1/2] cdrom: always check_disk

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Message-ID: <20110406121920.GC4142@mtj.dyndns.org>
Date:	Wed, 6 Apr 2011 05:20:09 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Amit Shah <amit.shah@...hat.com>,
	David Zeuthen <zeuthen@...il.com>,
	Martin Pitt <martin.pitt@...ntu.com>,
	Kay Sievers <kay.sievers@...y.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] cdrom: always check_disk_change() on open

cdrom_open() called check_disk_change() after the rest of open path
succeeded which leads to the following bizarre behavior.

* After media change, if the device opened without O_NONBLOCK,
  open_for_data() naturally fails with -ENOMEDIA and
  check_disk_change() is never called.  The media is known to be gone
  and the open failure makes it obvious to the userland but device
  invalidation never happens.

* But if the device is opened with O_NONBLOCK, all the checks are
  bypassed and cdrom_open() doesn't notice that the media is not there
  and check_disk_change() is called and invalidation happens.

There's nothing to be gained by avoiding calling check_disk_change()
on open failure.  Common cases end up calling check_disk_change()
anyway.  All we get is inconsistent behavior.

Fix it by moving check_disk_change() invocation to the top of
cdrom_open() so that it always gets called regardless of how the rest
of open proceeds.

Signed-off-by: Tejun Heo <tj@...nel.org>
Reported-by: Amit Shah <amit.shah@...hat.com>
Tested-by: Amit Shah <amit.shah@...hat.com>
---
 drivers/cdrom/cdrom.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/cdrom/cdrom.c b/drivers/cdrom/cdrom.c
index e2c48a7..5ade78a 100644
--- a/drivers/cdrom/cdrom.c
+++ b/drivers/cdrom/cdrom.c
@@ -986,6 +986,9 @@ int cdrom_open(struct cdrom_device_info *cdi, struct block_device *bdev, fmode_t

 	cdinfo(CD_OPEN, "entering cdrom_open\n"); 

+	/* open is event synchronization point, check events first */
+	check_disk_change(bdev);
+
 	/* if this was a O_NONBLOCK open and we should honor the flags,
 	 * do a quick open without drive/disc integrity checks. */
 	cdi->use_count++;
@@ -1012,9 +1015,6 @@ int cdrom_open(struct cdrom_device_info *cdi, struct block_device *bdev, fmode_t

 	cdinfo(CD_OPEN, "Use count for \"/dev/%s\" now %d\n",
 			cdi->name, cdi->use_count);
-	/* Do this on open.  Don't wait for mount, because they might
-	    not be mounting, but opening with O_NONBLOCK */
-	check_disk_change(bdev);
 	return 0;
 err_release:
 	if (CDROM_CAN(CDC_LOCK) && cdi->options & CDO_LOCK) {
--
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