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: __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 print_unlock_imbalance_bug.cold+0x114/0x123 lock_release+0x562/0xed0 up_write+0x2d/0x490 __do_sys_swapon+0x94b/0x3550 __x64_sys_swapon+0x54/0x80 do_syscall_64+0xa4/0x4b0 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x7f15da0a0dc7 Fixes: 1638045c ("mm: set S_SWAPFILE on blockdev swap devices") Signed-off-by: NNaohiro Aota <naohiro.aota@wdc.com> Signed-off-by: NAndrew Morton <akpm@linux-foundation.org> Tested-by: NQais Youef <qais.yousef@arm.com> Reviewed-by: NAndrew Morton <akpm@linux-foundation.org> Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/r/20200206090132.154869-1-naohiro.aota@wdc.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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