mm/swap: fix race on swap_info reuse between swapoff and swapon (f893ab41) · Commits · 戴 / test

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>

mm/swapfile.c

+10 −1

Original line number	Original line	Diff line number	Diff line
	@@ -1923,7 +1923,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
	p->swap_map = NULL;		p->swap_map = NULL;
	cluster_info = p->cluster_info;		cluster_info = p->cluster_info;
	p->cluster_info = NULL;		p->cluster_info = NULL;
	p->flags = 0;
	frontswap_map = frontswap_map_get(p);		frontswap_map = frontswap_map_get(p);
	spin_unlock(&p->lock);		spin_unlock(&p->lock);
	spin_unlock(&swap_lock);		spin_unlock(&swap_lock);
	@@ -1949,6 +1948,16 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
	mutex_unlock(&inode->i_mutex);		mutex_unlock(&inode->i_mutex);
	}		}
	filp_close(swap_file, NULL);		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;		err = 0;
	atomic_inc(&proc_poll_event);		atomic_inc(&proc_poll_event);
	wake_up_interruptible(&proc_poll_wait);		wake_up_interruptible(&proc_poll_wait);

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