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@xxxxxxxxxx>
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
---
mm/swapfile.c | 25 +++++++------------------
1 file changed, 7 insertions(+), 18 deletions(-)
--- 4.2-rc7/mm/swapfile.c 2015-07-05 19:25:02.852131158 -0700
+++ linux/mm/swapfile.c 2015-08-16 21:30:22.694123923 -0700
@@ -2143,11 +2143,10 @@ 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);
@@ -2348,7 +2347,6 @@ 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;
@@ -2388,19 +2386,8 @@ 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))
@@ -2433,6 +2420,8 @@ 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
@@ -2451,9 +2440,9 @@ 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);
}
}
--
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>