From 2130781e2aaab66e5a9f2fdc8af35da0153f405c Mon Sep 17 00:00:00 2001 From: Cesar Eduardo Barros Date: Tue, 22 Mar 2011 23:03:13 -0300 Subject: sys_swapon: fix inode locking A conflict between 52c50567d8ab ("mm: swap: unlock swapfile inode mutex before closing file on bad swapfiles") and 83ef99befc32 ("sys_swapon: remove did_down variable") caused a double unlock of the inode mutex (once in bad_swap: before the filp_close, once at the end just before returning). The patch which added the extra unlock cleared did_down to avoid unlocking twice, but the other patch removed the did_down variable. To fix, set inode to NULL after the first unlock, since it will be used after that point only for the final unlock. While checking this patch, I found a path which could unlock without locking, in case the same inode was added as a swapfile twice. To fix, move the setting of the inode variable further down, to just before claim_swapfile, which will lock the inode before doing anything else. Cc: Mel Gorman Cc: Hugh Dickins Cc: Eric B Munson Cc: KAMEZAWA Hiroyuki Cc: Andrew Morton Signed-off-by: Cesar Eduardo Barros Signed-off-by: Linus Torvalds --- mm/swapfile.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/mm/swapfile.c b/mm/swapfile.c index aafcf3611b31..71b42ec55b78 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -2088,7 +2088,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) p->swap_file = swap_file; mapping = swap_file->f_mapping; - inode = mapping->host; for (i = 0; i < nr_swapfiles; i++) { struct swap_info_struct *q = swap_info[i]; @@ -2101,6 +2100,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) } } + inode = mapping->host; + /* If S_ISREG(inode->i_mode) will do mutex_lock(&inode->i_mutex); */ error = claim_swapfile(p, inode); if (unlikely(error)) goto bad_swap; @@ -2187,8 +2188,10 @@ bad_swap: spin_unlock(&swap_lock); vfree(swap_map); if (swap_file) { - if (inode && S_ISREG(inode->i_mode)) + if (inode && S_ISREG(inode->i_mode)) { mutex_unlock(&inode->i_mutex); + inode = NULL; + } filp_close(swap_file, NULL); } out: -- cgit v1.2.3