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: 1638045c36 ("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>
66f10f5d58