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xfstest generic/587 reports a deadlock issue as below: ====================================================== WARNING: possible circular locking dependency detected 5.14.0-rc1 #69 Not tainted ------------------------------------------------------ repquota/8606 is trying to acquire lock: ffff888022ac9320 (&sb->s_type->i_mutex_key#18){+.+.}-{3:3}, at: f2fs_quota_sync+0x207/0x300 [f2fs] but task is already holding lock: ffff8880084bcde8 (&sbi->quota_sem){.+.+}-{3:3}, at: f2fs_quota_sync+0x59/0x300 [f2fs] which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&sbi->quota_sem){.+.+}-{3:3}: __lock_acquire+0x648/0x10b0 lock_acquire+0x128/0x470 down_read+0x3b/0x2a0 f2fs_quota_sync+0x59/0x300 [f2fs] f2fs_quota_on+0x48/0x100 [f2fs] do_quotactl+0x5e3/0xb30 __x64_sys_quotactl+0x23a/0x4e0 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae -> #1 (&sbi->cp_rwsem){++++}-{3:3}: __lock_acquire+0x648/0x10b0 lock_acquire+0x128/0x470 down_read+0x3b/0x2a0 f2fs_unlink+0x353/0x670 [f2fs] vfs_unlink+0x1c7/0x380 do_unlinkat+0x413/0x4b0 __x64_sys_unlinkat+0x50/0xb0 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae -> #0 (&sb->s_type->i_mutex_key#18){+.+.}-{3:3}: check_prev_add+0xdc/0xb30 validate_chain+0xa67/0xb20 __lock_acquire+0x648/0x10b0 lock_acquire+0x128/0x470 down_write+0x39/0xc0 f2fs_quota_sync+0x207/0x300 [f2fs] do_quotactl+0xaff/0xb30 __x64_sys_quotactl+0x23a/0x4e0 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae other info that might help us debug this: Chain exists of: &sb->s_type->i_mutex_key#18 --> &sbi->cp_rwsem --> &sbi->quota_sem Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&sbi->quota_sem); lock(&sbi->cp_rwsem); lock(&sbi->quota_sem); lock(&sb->s_type->i_mutex_key#18); *** DEADLOCK *** 3 locks held by repquota/8606: #0: ffff88801efac0e0 (&type->s_umount_key#53){++++}-{3:3}, at: user_get_super+0xd9/0x190 #1: ffff8880084bc380 (&sbi->cp_rwsem){++++}-{3:3}, at: f2fs_quota_sync+0x3e/0x300 [f2fs] #2: ffff8880084bcde8 (&sbi->quota_sem){.+.+}-{3:3}, at: f2fs_quota_sync+0x59/0x300 [f2fs] stack backtrace: CPU: 6 PID: 8606 Comm: repquota Not tainted 5.14.0-rc1 #69 Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006 Call Trace: dump_stack_lvl+0xce/0x134 dump_stack+0x17/0x20 print_circular_bug.isra.0.cold+0x239/0x253 check_noncircular+0x1be/0x1f0 check_prev_add+0xdc/0xb30 validate_chain+0xa67/0xb20 __lock_acquire+0x648/0x10b0 lock_acquire+0x128/0x470 down_write+0x39/0xc0 f2fs_quota_sync+0x207/0x300 [f2fs] do_quotactl+0xaff/0xb30 __x64_sys_quotactl+0x23a/0x4e0 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x7f883b0b4efe The root cause is ABBA deadlock of inode lock and cp_rwsem, reorder locks in f2fs_quota_sync() as below to fix this issue: - lock inode - lock cp_rwsem - lock quota_sem Fixes: db6ec53b7e03 ("f2fs: add a rw_sem to cover quota flag changes") Signed-off-by: Chao Yu <chao@kernel.org> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.