Commit f893ab41 authored Feb 06, 2014 by Weijie Yang Committed by Linus Torvalds Feb 06, 2014

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



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>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 579f8290

mm/swapfile.c

+10 −1

Original line number	Diff line number	Diff line
		@@ -1923,7 +1923,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
		p->swap_map = NULL;
		cluster_info = p->cluster_info;
		p->cluster_info = NULL;
		p->flags = 0;
		frontswap_map = frontswap_map_get(p);
		spin_unlock(&p->lock);
		spin_unlock(&swap_lock);
		@@ -1949,6 +1948,16 @@ 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);