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BUG: KCSAN: data-race in _copy_to_iter / vsnprintf

write to 0xffff888122ac8055 of 1 bytes by task 17688 on cpu 0:
 vsnprintf+0x815/0x8c0 lib/vsprintf.c:2981
 snprintf+0x86/0xb0 lib/vsprintf.c:3047
 ext4_multi_mount_protect+0x4eb/0x600 fs/ext4/mmp.c:381
 __ext4_fill_super fs/ext4/super.c:5531 [inline]
 ext4_fill_super+0x227f/0x37c0 fs/ext4/super.c:5865
 get_tree_bdev_flags+0x291/0x300 fs/super.c:1883
 get_tree_bdev+0x1f/0x30 fs/super.c:1906
 ext4_get_tree+0x1c/0x30 fs/ext4/super.c:5897
 vfs_get_tree+0x57/0x1d0 fs/super.c:1943
 fc_mount fs/namespace.c:1282 [inline]
 do_new_mount_fc fs/namespace.c:3910 [inline]
 do_new_mount+0x288/0x730 fs/namespace.c:3986
 path_mount+0x4ad/0xb90 fs/namespace.c:4337
 do_mount fs/namespace.c:4350 [inline]
 __do_sys_mount fs/namespace.c:4566 [inline]
 __se_sys_mount+0x28c/0x2e0 fs/namespace.c:4543
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4543
 x64_sys_call+0xc3b/0x2550 arch/x86/include/generated/asm/syscalls_64.h:166
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x112/0x360 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888122ac8000 of 512 bytes by task 14798 on cpu 1:
 instrument_copy_to_user include/linux/instrumented.h:130 [inline]
 copy_to_user_iter lib/iov_iter.c:24 [inline]
 iterate_ubuf include/linux/iov_iter.h:30 [inline]
 iterate_and_advance2 include/linux/iov_iter.h:302 [inline]
 iterate_and_advance include/linux/iov_iter.h:330 [inline]
 _copy_to_iter+0x130/0xea0 lib/iov_iter.c:197
 copy_page_to_iter+0x174/0x210 lib/iov_iter.c:374
 copy_folio_to_iter include/linux/uio.h:204 [inline]
 filemap_read+0x3fd/0xad0 mm/filemap.c:2875
 blkdev_read_iter+0x21e/0x2d0 block/fops.c:838
 new_sync_read fs/read_write.c:493 [inline]
 vfs_read+0x699/0x7c0 fs/read_write.c:574
 ksys_read+0xdc/0x1a0 fs/read_write.c:716
 __do_sys_read fs/read_write.c:725 [inline]
 __se_sys_read fs/read_write.c:723 [inline]
 __x64_sys_read+0x40/0x50 fs/read_write.c:723
 x64_sys_call+0x2135/0x2550 arch/x86/include/generated/asm/syscalls_64.h:1
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x112/0x360 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 14798 Comm: udevd Tainted: G S                  syzkaller #0 PREEMPT(lazy) 
Tainted: [S]=CPU_OUT_OF_SPEC
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/07/2026
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