Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 3.12 19/32] mm/swap: fix race on swap_info reuse between swapoff and swapon | Date | Tue, 18 Feb 2014 14:47:19 -0800 |
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3.12-stable review patch. If anyone has any objections, please let me know.
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From: Weijie Yang <weijie.yang@samsung.com>
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- mm/swapfile.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)
--- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1922,7 +1922,6 @@ SYSCALL_DEFINE1(swapoff, const char __us p->swap_map = NULL; cluster_info = p->cluster_info; p->cluster_info = NULL; - p->flags = 0; frontswap_map = frontswap_map_get(p); frontswap_map_set(p, NULL); spin_unlock(&p->lock); @@ -1948,6 +1947,16 @@ SYSCALL_DEFINE1(swapoff, const char __us 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);
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