Messages in this thread Patch in this message | | | From | Luis Henriques <> | Subject | [PATCH 3.5 13/60] mm/swap: fix race on swap_info reuse between swapoff and swapon | Date | Fri, 21 Feb 2014 13:00:40 +0000 |
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3.5.7.31 -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> [ luis: backported to 3.5: adjusted context ] Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- mm/swapfile.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/mm/swapfile.c b/mm/swapfile.c index 71373d0..222928f 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1642,7 +1642,6 @@ 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); @@ -1662,6 +1661,16 @@ 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); -- 1.9.0
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