Commit f893ab41 authored by Weijie Yang's avatar Weijie Yang Committed by Linus Torvalds

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: default avatarWeijie Yang <weijie.yang@samsung.com>
Acked-by: default avatarHugh Dickins <hughd@google.com>
Cc: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 579f8290
...@@ -1923,7 +1923,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) ...@@ -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) ...@@ -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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