CVE-2024-26658: In the Linux kernel, the following vulnerability has been resolved:  bcachefs: grab s_umount only if snapshotting  When I was testing mongodb over bcachefs with compression, there is a lockdep warning when snapshotting mongodb data volume.  $ cat test.sh prog=bcachefs  $prog subvolume create /mnt/data $prog subvolume create /mnt/data/snapshots  while true;do     $prog subvolume snapshot /mnt/data /mnt/data/snapshots/$(date +%s)     sleep 1s done  $ cat /etc/mongodb.conf systemLog:   destination: file   logAppend: true   path: /mnt/data/mongod.log  storage:   dbPath: /mnt/data/  lockdep reports: [ 3437.452330] ====================================================== [ 3437.452750] WARNING: possible circular locking dependency detected [ 3437.453168] 6.7.0-rc7-custom+ #85 Tainted: G            E [ 3437.453562] ------------------------------------------------------ [ 3437.453981] bcachefs/35533 is trying to acquire lock: [ 3437.454325] ffffa0a02b2b1418 (sb_writers#10){.+.+}-{0:0}, at: filename_create+0x62/0x190 [ 3437.454875]                but task is already holding lock: [ 3437.455268] ffffa0a02b2b10e0 (&type->s_umount_key#48){.+.+}-{3:3}, at: bch2_fs_file_ioctl+0x232/0xc90 [bcachefs] [ 3437.456009]                which lock already depends on the new lock.  [ 3437.456553]                the existing dependency chain (in reverse order) is: [ 3437.457054]                -> #3 (&type->s_umount_key#48){.+.+}-{3:3}: [ 3437.457507]        down_read+0x3e/0x170 [ 3437.457772]        bch2_fs_file_ioctl+0x232/0xc90 [bcachefs] [ 3437.458206]        __x64_sys_ioctl+0x93/0xd0 [ 3437.458498]        do_syscall_64+0x42/0xf0 [ 3437.458779]        entry_SYSCALL_64_after_hwframe+0x6e/0x76 [ 3437.459155]                -> #2 (&c->snapshot_create_lock){++++}-{3:3}: [ 3437.459615]        down_read+0x3e/0x170 [ 3437.459878]        bch2_truncate+0x82/0x110 [bcachefs] [ 3437.460276]        bchfs_truncate+0x254/0x3c0 [bcachefs] [ 3437.460686]        notify_change+0x1f1/0x4a0 [ 3437.461283]        do_truncate+0x7f/0xd0 [ 3437.461555]        path_openat+0xa57/0xce0 [ 3437.461836]        do_filp_open+0xb4/0x160 [ 3437.462116]        do_sys_openat2+0x91/0xc0 [ 3437.462402]        __x64_sys_openat+0x53/0xa0 [ 3437.462701]        do_syscall_64+0x42/0xf0 [ 3437.462982]        entry_SYSCALL_64_after_hwframe+0x6e/0x76 [ 3437.463359]                -> #1 (&sb->s_type->i_mutex_key#15){+.+.}-{3:3}: [ 3437.463843]        down_write+0x3b/0xc0 [ 3437.464223]        bch2_write_iter+0x5b/0xcc0 [bcachefs] [ 3437.464493]        vfs_write+0x21b/0x4c0 [ 3437.464653]        ksys_write+0x69/0xf0 [ 3437.464839]        do_syscall_64+0x42/0xf0 [ 3437.465009]        entry_SYSCALL_64_after_hwframe+0x6e/0x76 [ 3437.465231]                -> #0 (sb_writers#10){.+.+}-{0:0}: [ 3437.465471]        __lock_acquire+0x1455/0x21b0 [ 3437.465656]        lock_acquire+0xc6/0x2b0 [ 3437.465822]        mnt_want_write+0x46/0x1a0 [ 3437.465996]        filename_create+0x62/0x190 [ 3437.466175]        user_path_create+0x2d/0x50 [ 3437.466352]        bch2_fs_file_ioctl+0x2ec/0xc90 [bcachefs] [ 3437.466617]        __x64_sys_ioctl+0x93/0xd0 [ 3437.466791]        do_syscall_64+0x42/0xf0 [ 3437.466957]        entry_SYSCALL_64_after_hwframe+0x6e/0x76 [ 3437.467180]                other info that might help us debug this:  [ 3437.469670] 2 locks held by bcachefs/35533:                other info that might help us debug this:  [ 3437.467507] Chain exists of:                  sb_writers#10 --> &c->snapshot_create_lock --> &type->s_umount_key#48  [ 3437.467979]  Possible unsafe locking scenario:  [ 3437.468223]        CPU0                    CPU1 [ 3437.468405]        ----                    ---- [ 3437.468585]   rlock(&type->s_umount_key#48); [ 3437.468758]                                lock(&c->snapshot_create_lock); [ 3437.469030]                                lock(&type->s_umount_key#48); [ 3437.469291]   rlock(sb_writers#10); [ 3437.469434]                 *** DEADLOCK ***  [ 3437.469 ---truncated---