3.16.70-rc1 review patch. If anyone has any objections, please let me know.
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From: Hugh Dickins hughd@google.com
commit 6f179af88f60b32c2855e7f3e16ea8e336a7043f upstream.
While running KernelThreadSanitizer (ktsan) on upstream kernel with trinity, we got a few reports from SyS_swapon, here is one of them:
Read of size 8 by thread T307 (K7621): [< inlined >] SyS_swapon+0x3c0/0x1850 SYSC_swapon mm/swapfile.c:2395 [<ffffffff812242c0>] SyS_swapon+0x3c0/0x1850 mm/swapfile.c:2345 [<ffffffff81e97c8a>] ia32_do_call+0x1b/0x25
Looks like the swap_lock should be taken when iterating through the swap_info array on lines 2392 - 2401: q->swap_file may be reset to NULL by another thread before it is dereferenced for f_mapping.
But why is that iteration needed at all? Doesn't the claim_swapfile() which follows do all that is needed to check for a duplicate entry - FMODE_EXCL on a bdev, testing IS_SWAPFILE under i_mutex on a regfile?
Well, not quite: bd_may_claim() allows the same "holder" to claim the bdev again, so we do need to use a different holder than "sys_swapon"; and we should not replace appropriate -EBUSY by inappropriate -EINVAL.
Index i was reused in a cpu loop further down: renamed cpu there.
Reported-by: Andrey Konovalov andreyknvl@google.com Signed-off-by: Hugh Dickins hughd@google.com Signed-off-by: Al Viro viro@zeniv.linux.org.uk Signed-off-by: Ben Hutchings ben@decadent.org.uk --- mm/swapfile.c | 25 +++++++------------------ 1 file changed, 7 insertions(+), 18 deletions(-)
--- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -2144,11 +2144,10 @@ static int claim_swapfile(struct swap_in if (S_ISBLK(inode->i_mode)) { p->bdev = bdgrab(I_BDEV(inode)); error = blkdev_get(p->bdev, - FMODE_READ | FMODE_WRITE | FMODE_EXCL, - sys_swapon); + FMODE_READ | FMODE_WRITE | FMODE_EXCL, p); if (error < 0) { p->bdev = NULL; - return -EINVAL; + return error; } p->old_block_size = block_size(p->bdev); error = set_blocksize(p->bdev, PAGE_SIZE); @@ -2365,7 +2364,6 @@ SYSCALL_DEFINE2(swapon, const char __use struct filename *name; struct file *swap_file = NULL; struct address_space *mapping; - int i; int prio; int error; union swap_header *swap_header; @@ -2405,19 +2403,8 @@ SYSCALL_DEFINE2(swapon, const char __use
p->swap_file = swap_file; mapping = swap_file->f_mapping; - - for (i = 0; i < nr_swapfiles; i++) { - struct swap_info_struct *q = swap_info[i]; - - if (q == p || !q->swap_file) - continue; - if (mapping == q->swap_file->f_mapping) { - error = -EBUSY; - goto bad_swap; - } - } - inode = mapping->host; + /* If S_ISREG(inode->i_mode) will do mutex_lock(&inode->i_mutex); */ error = claim_swapfile(p, inode); if (unlikely(error)) @@ -2450,6 +2437,8 @@ SYSCALL_DEFINE2(swapon, const char __use goto bad_swap; } if (p->bdev && blk_queue_nonrot(bdev_get_queue(p->bdev))) { + int cpu; + p->flags |= SWP_SOLIDSTATE; /* * select a random position to start with to help wear leveling @@ -2468,9 +2457,9 @@ SYSCALL_DEFINE2(swapon, const char __use error = -ENOMEM; goto bad_swap; } - for_each_possible_cpu(i) { + for_each_possible_cpu(cpu) { struct percpu_cluster *cluster; - cluster = per_cpu_ptr(p->percpu_cluster, i); + cluster = per_cpu_ptr(p->percpu_cluster, cpu); cluster_set_null(&cluster->index); } }