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BUG: KCSAN: data-race in ext4_mb_scan_group / mb_mark_used

read-write to 0xffff88810041743c of 4 bytes by task 3538 on cpu 0:
 mb_mark_used+0x129/0xda0 fs/ext4/mballoc.c:2166
 ext4_mb_use_best_found+0xf5/0x2c0 fs/ext4/mballoc.c:2248
 ext4_mb_check_limits fs/ext4/mballoc.c:2312 [inline]
 ext4_mb_complex_scan_group+0x804/0x870 fs/ext4/mballoc.c:2632
 __ext4_mb_scan_group fs/ext4/mballoc.c:2700 [inline]
 ext4_mb_scan_group+0xcc1/0xf20 fs/ext4/mballoc.c:2991
 ext4_mb_scan_groups_linear fs/ext4/mballoc.c:1176 [inline]
 ext4_mb_scan_groups fs/ext4/mballoc.c:1208 [inline]
 ext4_mb_regular_allocator+0x696/0x16d0 fs/ext4/mballoc.c:3062
 ext4_mb_new_blocks+0x7db/0x1f50 fs/ext4/mballoc.c:6316
 ext4_ext_map_blocks+0xdc9/0x2ff0 fs/ext4/extents.c:4461
 ext4_map_create_blocks+0xce/0x3a0 fs/ext4/inode.c:626
 ext4_map_blocks+0x594/0x970 fs/ext4/inode.c:819
 ext4_getblk+0x128/0x530 fs/ext4/inode.c:987
 ext4_bread+0x28/0x110 fs/ext4/inode.c:1050
 ext4_append+0x181/0x2c0 fs/ext4/namei.c:83
 ext4_init_new_dir+0xec/0x180 fs/ext4/namei.c:2979
 ext4_mkdir+0x31e/0x740 fs/ext4/namei.c:3015
 vfs_mkdir+0x294/0x3e0 fs/namei.c:5239
 filename_mkdirat+0x138/0x300 fs/namei.c:5272
 __do_sys_mkdirat fs/namei.c:5293 [inline]
 __se_sys_mkdirat+0x32/0xf0 fs/namei.c:5290
 __x64_sys_mkdirat+0x43/0x50 fs/namei.c:5290
 x64_sys_call+0x2c4e/0x3020 arch/x86/include/generated/asm/syscalls_64.h:259
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810041743c of 4 bytes by task 21016 on cpu 1:
 ext4_mb_good_group_nolock fs/ext4/mballoc.c:2795 [inline]
 ext4_mb_scan_group+0x470/0xf20 fs/ext4/mballoc.c:2970
 ext4_mb_scan_groups_linear fs/ext4/mballoc.c:1176 [inline]
 ext4_mb_scan_groups fs/ext4/mballoc.c:1208 [inline]
 ext4_mb_regular_allocator+0x696/0x16d0 fs/ext4/mballoc.c:3062
 ext4_mb_new_blocks+0x7db/0x1f50 fs/ext4/mballoc.c:6316
 ext4_ext_map_blocks+0xdc9/0x2ff0 fs/ext4/extents.c:4461
 ext4_map_create_blocks+0xce/0x3a0 fs/ext4/inode.c:626
 ext4_map_blocks+0x594/0x970 fs/ext4/inode.c:819
 ext4_getblk+0x128/0x530 fs/ext4/inode.c:987
 ext4_bread+0x28/0x110 fs/ext4/inode.c:1050
 ext4_append+0x181/0x2c0 fs/ext4/namei.c:83
 ext4_init_new_dir+0xec/0x180 fs/ext4/namei.c:2979
 ext4_mkdir+0x31e/0x740 fs/ext4/namei.c:3015
 vfs_mkdir+0x294/0x3e0 fs/namei.c:5239
 filename_mkdirat+0x138/0x300 fs/namei.c:5272
 __do_sys_mkdirat fs/namei.c:5293 [inline]
 __se_sys_mkdirat+0x32/0xf0 fs/namei.c:5290
 __x64_sys_mkdirat+0x43/0x50 fs/namei.c:5290
 x64_sys_call+0x2c4e/0x3020 arch/x86/include/generated/asm/syscalls_64.h:259
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x000007c6 -> 0x000007c5

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 21016 Comm: syz-executor.4 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
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/dev/loop4: Can't open blockdev