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BUG: KCSAN: data-race in _copy_to_iter / strncpy

write to 0xffff888146838488 of 1 bytes by task 24849 on cpu 0:
 strncpy+0x9b/0x150 lib/string.c:96
 ext4_sample_last_mounted fs/ext4/file.c:861 [inline]
 ext4_file_open+0x361/0x3f0 fs/ext4/file.c:880
 do_dentry_open+0x5b3/0x930 fs/open.c:920
 vfs_open+0x47/0x50 fs/open.c:1051
 do_open fs/namei.c:3560 [inline]
 path_openat+0x17e6/0x1d00 fs/namei.c:3715
 do_filp_open+0xf6/0x200 fs/namei.c:3742
 do_sys_openat2+0xb5/0x2a0 fs/open.c:1348
 do_sys_open fs/open.c:1364 [inline]
 __do_sys_open fs/open.c:1372 [inline]
 __se_sys_open fs/open.c:1368 [inline]
 __x64_sys_open+0xe6/0x110 fs/open.c:1368
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffff888146838400 of 1024 bytes by task 3224 on cpu 1:
 instrument_copy_to_user include/linux/instrumented.h:120 [inline]
 copyout lib/iov_iter.c:169 [inline]
 _copy_to_iter+0x136/0x8f0 lib/iov_iter.c:523
 copy_page_to_iter+0x1a8/0x310 lib/iov_iter.c:721
 copy_folio_to_iter include/linux/uio.h:174 [inline]
 filemap_read+0x438/0x680 mm/filemap.c:2745
 blkdev_read_iter+0x2ca/0x370 block/fops.c:606
 call_read_iter include/linux/fs.h:1845 [inline]
 new_sync_read fs/read_write.c:389 [inline]
 vfs_read+0x39a/0x560 fs/read_write.c:470
 ksys_read+0xeb/0x1a0 fs/read_write.c:613
 __do_sys_read fs/read_write.c:623 [inline]
 __se_sys_read fs/read_write.c:621 [inline]
 __x64_sys_read+0x42/0x50 fs/read_write.c:621
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 3224 Comm: udevd Not tainted 6.3.0-rc5-syzkaller-00202-ga79d5c76f705 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/30/2023
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