Hugh, I am awaiting your feedback on this one please. From: Weijie Yang <weijie.yang@xxxxxxxxxxx> Subject: 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@xxxxxxxxxxxxxxxxxxxx: tidy up code comment] Signed-off-by: Weijie Yang <weijie.yang@xxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/swapfile.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff -puN mm/swapfile.c~mm-swap-fix-race-on-swap_info-reuse-between-swapoff-and-swapon mm/swapfile.c --- a/mm/swapfile.c~mm-swap-fix-race-on-swap_info-reuse-between-swapoff-and-swapon +++ a/mm/swapfile.c @@ -1923,7 +1923,6 @@ 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); spin_unlock(&p->lock); spin_unlock(&swap_lock); @@ -1949,6 +1948,16 @@ 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); _ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>