Re: [f2fs-dev] [PATCH v2] f2fs: fix to avoid mmap vs set_compress_option case

From: Eric Biggers
Date: Fri Jun 16 2023 - 02:03:53 EST

Hi Chao,

On Mon, May 29, 2023 at 06:47:09PM +0800, Chao Yu wrote:
> Compression option in inode should not be changed after they have
> been used, however, it may happen in below race case:
>
> Thread A Thread B
> - f2fs_ioc_set_compress_option
> - check f2fs_is_mmap_file()
> - check get_dirty_pages()
> - check F2FS_HAS_BLOCKS()
> - f2fs_file_mmap
> - set_inode_flag(FI_MMAP_FILE)
> - fault
> - do_page_mkwrite
> - f2fs_vm_page_mkwrite
> - f2fs_get_block_locked
> - fault_dirty_shared_page
> - set_page_dirty
> - update i_compress_algorithm
> - update i_log_cluster_size
> - update i_cluster_size
>
> Avoid such race condition by covering f2fs_file_mmap() w/ inode lock,
> meanwhile add mmap file check condition in f2fs_may_compress() as well.
>
> Fixes: e1e8debec656 ("f2fs: add F2FS_IOC_SET_COMPRESS_OPTION ioctl")
> Signed-off-by: Chao Yu <chao@xxxxxxxxxx>

This patch causes the following deadlock report:

[ 9.622928] ======================================================
[ 9.623484] WARNING: possible circular locking dependency detected
[ 9.624054] 6.4.0-rc1-00039-g18a87f3eaef5 #12 Tainted: G T
[ 9.624672] ------------------------------------------------------
[ 9.625242] xfs_io/2440 is trying to acquire lock:
[ 9.625682] ffff888103a2c888 (&sb->s_type->i_mutex_key#11){+.+.}-{3:3}, at: f2fs_file_mmap+0x53/0xc0
[ 9.626523]
[ 9.626523] but task is already holding lock:
[ 9.627058] ffff888103d0e8c0 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0x72/0x1c0
[ 9.627797]
[ 9.627797] which lock already depends on the new lock.
[ 9.627797]
[ 9.628528]
[ 9.628528] the existing dependency chain (in reverse order) is:
[ 9.629210]
[ 9.629210] -> #1 (&mm->mmap_lock){++++}-{3:3}:
[ 9.629761] lock_acquire+0xcb/0x2d0
[ 9.630147] __might_fault+0x6f/0xa0
[ 9.630526] _copy_to_user+0x27/0x90
[ 9.630915] fiemap_fill_next_extent+0xbe/0x130
[ 9.631378] f2fs_fiemap+0x223/0x5c0
[ 9.631757] do_vfs_ioctl+0x6d5/0x860
[ 9.632150] __x64_sys_ioctl+0x4a/0xd0
[ 9.632547] do_syscall_64+0x39/0x90
[ 9.632935] entry_SYSCALL_64_after_hwframe+0x63/0xcd
[ 9.633444]
[ 9.633444] -> #0 (&sb->s_type->i_mutex_key#11){+.+.}-{3:3}:
[ 9.634104] check_prev_add+0x93/0xbd0
[ 9.634500] __lock_acquire+0xc27/0x11e0
[ 9.634918] lock_acquire+0xcb/0x2d0
[ 9.635297] down_write+0x3d/0x100
[ 9.635660] f2fs_file_mmap+0x53/0xc0
[ 9.636053] mmap_region+0x20b/0x920
[ 9.636433] do_mmap+0x345/0x570
[ 9.636781] vm_mmap_pgoff+0xa1/0x1c0
[ 9.637179] ksys_mmap_pgoff+0xa0/0xc0
[ 9.637574] __x64_sys_mmap+0x32/0x60
[ 9.637970] do_syscall_64+0x39/0x90
[ 9.638348] entry_SYSCALL_64_after_hwframe+0x63/0xcd
[ 9.638864]
[ 9.638864] other info that might help us debug this:
[ 9.638864]
[ 9.639582] Possible unsafe locking scenario:
[ 9.639582]
[ 9.640128] CPU0 CPU1
[ 9.640545] ---- ----
[ 9.640971] lock(&mm->mmap_lock);
[ 9.641298] lock(&sb->s_type->i_mutex_key#11);
[ 9.641953] lock(&mm->mmap_lock);
[ 9.642500] lock(&sb->s_type->i_mutex_key#11);
[ 9.642930]
[ 9.642930] *** DEADLOCK ***
[ 9.642930]
[ 9.643469] 1 lock held by xfs_io/2440:
[ 9.643830] #0: ffff888103d0e8c0 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0x72/0x1c0
[ 9.644600]
[ 9.644600] stack backtrace:
[ 9.645012] CPU: 0 PID: 2440 Comm: xfs_io Tainted: G T 6.4.0-rc1-00039-g18a87f3eaef5 #12
[ 9.645869] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS Arch Linux 1.16.2-1-1 04/01/2014
[ 9.646697] Call Trace:
[ 9.646933] <TASK>
[ 9.647137] dump_stack_lvl+0x4e/0x90
[ 9.647483] dump_stack+0x14/0x20
[ 9.647800] print_circular_bug+0x2eb/0x440
[ 9.648188] check_noncircular+0x124/0x140
[ 9.648568] check_prev_add+0x93/0xbd0
[ 9.648923] ? add_chain_cache+0x10e/0x470
[ 9.649304] __lock_acquire+0xc27/0x11e0
[ 9.649670] lock_acquire+0xcb/0x2d0
[ 9.650013] ? f2fs_file_mmap+0x53/0xc0
[ 9.650372] down_write+0x3d/0x100
[ 9.650696] ? f2fs_file_mmap+0x53/0xc0
[ 9.651059] f2fs_file_mmap+0x53/0xc0
[ 9.651402] mmap_region+0x20b/0x920
[ 9.651739] do_mmap+0x345/0x570
[ 9.652053] vm_mmap_pgoff+0xa1/0x1c0
[ 9.652397] ksys_mmap_pgoff+0xa0/0xc0
[ 9.652747] __x64_sys_mmap+0x32/0x60
[ 9.653098] do_syscall_64+0x39/0x90
[ 9.653432] entry_SYSCALL_64_after_hwframe+0x63/0xcd
[ 9.653904] RIP: 0033:0x7f1366f92b62
[ 9.654237] Code: e4 e8 b2 4b 01 00 66 90 41 f7 c1 ff 0f 00 00 75 27 55 48 89 fd 53 89 cb 48 85 ff 74 3b 41 89 da 48 89 ef 4
[ 9.655918] RSP: 002b:00007ffd5de38f08 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
[ 9.656601] RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007f1366f92b62
[ 9.657256] RDX: 0000000000000001 RSI: 0000000000020000 RDI: 0000000000000000
[ 9.657909] RBP: 0000000000000000 R08: 0000000000000003 R09: 0000000000000000
[ 9.658558] R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000
[ 9.659215] R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000020000
[ 9.659867] </TASK>