From: Naohiro Aota naohiro.aota@wdc.com Subject: mm/swapfile.c: move inode_lock out of claim_swapfile

claim_swapfile() currently keeps the inode locked when it is successful, or the file is already swapfile (with -EBUSY). And, on the other error cases, it does not lock the inode.

This inconsistency of the lock state and return value is quite confusing and actually causing a bad unlock balance as below in the "bad_swap" section of __do_sys_swapon().

This commit fixes this issue by moving the inode_lock() and IS_SWAPFILE check out of claim_swapfile(). The inode is unlocked in "bad_swap_unlock_inode" section, so that the inode is ensured to be unlocked at "bad_swap". Thus, error handling codes after the locking now jumps to "bad_swap_unlock_inode" instead of "bad_swap".

===================================== WARNING: bad unlock balance detected! 5.5.0-rc7+ #176 Not tainted ------------------------------------- swapon/4294 is trying to release lock (&sb->s_type->i_mutex_key) at: [<ffffffff8173a6eb>] __do_sys_swapon+0x94b/0x3550 but there are no more locks to release!

other info that might help us debug this: no locks held by swapon/4294.

stack backtrace: CPU: 5 PID: 4294 Comm: swapon Not tainted 5.5.0-rc7-BTRFS-ZNS+ #176 Hardware name: ASUS All Series/H87-PRO, BIOS 2102 07/29/2014 Call Trace: dump_stack+0xa1/0xea ? __do_sys_swapon+0x94b/0x3550 print_unlock_imbalance_bug.cold+0x114/0x123 ? __do_sys_swapon+0x94b/0x3550 lock_release+0x562/0xed0 ? kvfree+0x31/0x40 ? lock_downgrade+0x770/0x770 ? kvfree+0x31/0x40 ? rcu_read_lock_sched_held+0xa1/0xd0 ? rcu_read_lock_bh_held+0xb0/0xb0 up_write+0x2d/0x490 ? kfree+0x293/0x2f0 __do_sys_swapon+0x94b/0x3550 ? putname+0xb0/0xf0 ? kmem_cache_free+0x2e7/0x370 ? do_sys_open+0x184/0x3e0 ? generic_max_swapfile_size+0x40/0x40 ? do_syscall_64+0x27/0x4b0 ? entry_SYSCALL_64_after_hwframe+0x49/0xbe ? lockdep_hardirqs_on+0x38c/0x590 __x64_sys_swapon+0x54/0x80 do_syscall_64+0xa4/0x4b0 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x7f15da0a0dc7

Link: http://lkml.kernel.org/r/20200206090132.154869-1-naohiro.aota@wdc.com Fixes: 1638045c3677 ("mm: set S_SWAPFILE on blockdev swap devices") Signed-off-by: Naohiro Aota naohiro.aota@wdc.com Reviewed-by: Andrew Morton akpm@linux-foundation.org Reviewed-by: Darrick J. Wong darrick.wong@oracle.com Tested-by: Qais Youef qais.yousef@arm.com Cc: Christoph Hellwig hch@infradead.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/swapfile.c | 41 ++++++++++++++++++++--------------------- 1 file changed, 20 insertions(+), 21 deletions(-)

--- a/mm/swapfile.c~mm-swap-move-inode_lock-out-of-claim_swapfile +++ a/mm/swapfile.c @@ -2899,10 +2899,6 @@ static int claim_swapfile(struct swap_in p->bdev = inode->i_sb->s_bdev; }

- inode_lock(inode); - if (IS_SWAPFILE(inode)) - return -EBUSY; - return 0; }

@@ -3157,36 +3153,41 @@ SYSCALL_DEFINE2(swapon, const char __use mapping = swap_file->f_mapping; inode = mapping->host;

- /* will take i_rwsem; */ error = claim_swapfile(p, inode); if (unlikely(error)) goto bad_swap;

+ inode_lock(inode); + if (IS_SWAPFILE(inode)) { + error = -EBUSY; + goto bad_swap_unlock_inode; + } + /* * Read the swap header. */ if (!mapping->a_ops->readpage) { error = -EINVAL; - goto bad_swap; + goto bad_swap_unlock_inode; } page = read_mapping_page(mapping, 0, swap_file); if (IS_ERR(page)) { error = PTR_ERR(page); - goto bad_swap; + goto bad_swap_unlock_inode; } swap_header = kmap(page);

maxpages = read_swap_header(p, swap_header, inode); if (unlikely(!maxpages)) { error = -EINVAL; - goto bad_swap; + goto bad_swap_unlock_inode; }

/* OK, set up the swap map and apply the bad block list */ swap_map = vzalloc(maxpages); if (!swap_map) { error = -ENOMEM; - goto bad_swap; + goto bad_swap_unlock_inode; }

if (bdi_cap_stable_pages_required(inode_to_bdi(inode))) @@ -3211,7 +3212,7 @@ SYSCALL_DEFINE2(swapon, const char __use GFP_KERNEL); if (!cluster_info) { error = -ENOMEM; - goto bad_swap; + goto bad_swap_unlock_inode; }

for (ci = 0; ci < nr_cluster; ci++) @@ -3220,7 +3221,7 @@ SYSCALL_DEFINE2(swapon, const char __use p->percpu_cluster = alloc_percpu(struct percpu_cluster); if (!p->percpu_cluster) { error = -ENOMEM; - goto bad_swap; + goto bad_swap_unlock_inode; } for_each_possible_cpu(cpu) { struct percpu_cluster *cluster; @@ -3234,13 +3235,13 @@ SYSCALL_DEFINE2(swapon, const char __use

error = swap_cgroup_swapon(p->type, maxpages); if (error) - goto bad_swap; + goto bad_swap_unlock_inode;

nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map, cluster_info, maxpages, &span); if (unlikely(nr_extents < 0)) { error = nr_extents; - goto bad_swap; + goto bad_swap_unlock_inode; } /* frontswap enabled? set up bit-per-page map for frontswap */ if (IS_ENABLED(CONFIG_FRONTSWAP)) @@ -3280,7 +3281,7 @@ SYSCALL_DEFINE2(swapon, const char __use

error = init_swap_address_space(p->type, maxpages); if (error) - goto bad_swap; + goto bad_swap_unlock_inode;

/* * Flush any pending IO and dirty mappings before we start using this @@ -3290,7 +3291,7 @@ SYSCALL_DEFINE2(swapon, const char __use error = inode_drain_writes(inode); if (error) { inode->i_flags &= ~S_SWAPFILE; - goto bad_swap; + goto bad_swap_unlock_inode; }

mutex_lock(&swapon_mutex); @@ -3315,6 +3316,8 @@ SYSCALL_DEFINE2(swapon, const char __use

error = 0; goto out; +bad_swap_unlock_inode: + inode_unlock(inode); bad_swap: free_percpu(p->percpu_cluster); p->percpu_cluster = NULL; @@ -3322,6 +3325,7 @@ bad_swap: set_blocksize(p->bdev, p->old_block_size); blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL); } + inode = NULL; destroy_swap_extents(p); swap_cgroup_swapoff(p->type); spin_lock(&swap_lock); @@ -3333,13 +3337,8 @@ bad_swap: kvfree(frontswap_map); if (inced_nr_rotate_swap) atomic_dec(&nr_rotate_swap); - if (swap_file) { - if (inode) { - inode_unlock(inode); - inode = NULL; - } + if (swap_file) filp_close(swap_file, NULL); - } out: if (page && !IS_ERR(page)) { kunmap(page); _