diff mbox

[3.8.y.z,extended,stable] Patch "mm/swap: fix race on swap_info reuse between swapoff and swapon" has been added to staging queue

Message ID 1392932280-26058-1-git-send-email-kamal@canonical.com
State New
Headers show

Commit Message

Kamal Mostafa Feb. 20, 2014, 9:38 p.m. UTC 
This is a note to let you know that I have just added a patch titled

    mm/swap: fix race on swap_info reuse between swapoff and swapon

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.19.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

From fbdc052c46f4dd3ecdea252ccee5360f0a70548c Mon Sep 17 00:00:00 2001
From: Weijie Yang <weijie.yang@samsung.com>
Date: Thu, 6 Feb 2014 12:04:23 -0800
Subject: mm/swap: fix race on swap_info reuse between swapoff and swapon

commit f893ab41e4dae2fe8991faf5d86d029068d1ef3a upstream.

swapoff clear swap_info's SWP_USED flag prematurely and free its
resources after that.  A concurrent swapon will reuse this swap_info
while its previous resources are not cleared completely.

These late freed resources are:
 - p->percpu_cluster
 - swap_cgroup_ctrl[type]
 - block_device setting
 - inode->i_flags &= ~S_SWAPFILE

This patch clears the SWP_USED flag after all its resources are freed,
so that swapon can reuse this swap_info by alloc_swap_info() safely.

[akpm@linux-foundation.org: tidy up code comment]
Signed-off-by: Weijie Yang <weijie.yang@samsung.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 mm/swapfile.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

--
1.8.3.2
diff mbox

Patch

diff --git a/mm/swapfile.c b/mm/swapfile.c
index e97a0e5..85c5777 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1587,7 +1587,6 @@  SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	p->max = 0;
 	swap_map = p->swap_map;
 	p->swap_map = NULL;
-	p->flags = 0;
 	frontswap_invalidate_area(type);
 	spin_unlock(&swap_lock);
 	mutex_unlock(&swapon_mutex);
@@ -1607,6 +1606,16 @@  SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 		mutex_unlock(&inode->i_mutex);
 	}
 	filp_close(swap_file, NULL);
+
+	/*
+	 * Clear the SWP_USED flag after all resources are freed so that swapon
+	 * can reuse this swap_info in alloc_swap_info() safely.  It is ok to
+	 * not hold p->lock after we cleared its SWP_WRITEOK.
+	 */
+	spin_lock(&swap_lock);
+	p->flags = 0;
+	spin_unlock(&swap_lock);
+
 	err = 0;
 	atomic_inc(&proc_poll_event);
 	wake_up_interruptible(&proc_poll_wait);