syzbot

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BUG: KCSAN: data-race in __fat_fs_error / atime_needs_update

write to 0xffff88814a6b7050 of 8 bytes by task 26939 on cpu 1:
 __fat_fs_error+0x14e/0x191 fs/fat/misc.c:38
 fat_validate_dir fs/fat/inode.c:508 [inline]
 fat_fill_inode+0x9d7/0x9f0 fs/fat/inode.c:541
 fat_build_inode+0x134/0x1a0 fs/fat/inode.c:607
 vfat_lookup+0x1d9/0x300 fs/fat/namei_vfat.c:721
 __lookup_slow+0x181/0x280 fs/namei.c:1629
 lookup_slow fs/namei.c:1646 [inline]
 walk_component+0x2a5/0x350 fs/namei.c:1942
 link_path_walk+0x4ba/0x780 fs/namei.c:2265
 path_lookupat+0x7b/0x570 fs/namei.c:2420
 filename_lookup+0xff/0x390 fs/namei.c:2454
 user_path_at_empty+0x3b/0x50 fs/namei.c:2734
 user_path_at include/linux/namei.h:60 [inline]
 do_sys_truncate fs/open.c:133 [inline]
 __do_sys_truncate fs/open.c:147 [inline]
 __se_sys_truncate fs/open.c:145 [inline]
 __x64_sys_truncate+0x75/0x120 fs/open.c:145
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88814a6b7050 of 8 bytes by task 26921 on cpu 0:
 atime_needs_update+0xb5/0x390 fs/inode.c:1811
 touch_atime+0x54/0x240 fs/inode.c:1838
 file_accessed include/linux/fs.h:2456 [inline]
 generic_file_splice_read+0x284/0x310 fs/splice.c:314
 do_splice_to fs/splice.c:796 [inline]
 splice_direct_to_actor+0x2aa/0x650 fs/splice.c:870
 do_splice_direct+0xf5/0x170 fs/splice.c:979
 do_sendfile+0x773/0xda0 fs/read_write.c:1260
 __do_sys_sendfile64 fs/read_write.c:1325 [inline]
 __se_sys_sendfile64 fs/read_write.c:1311 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1311
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 26921 Comm: syz-executor.3 Not tainted 5.13.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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FAT-fs (loop3): error, fat_get_cluster: invalid cluster chain (i_pos 52)
FAT-fs (loop3): error, fat_get_cluster: invalid cluster chain (i_pos 52)