syzbot

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BUG: KCSAN: data-race in d_make_discardable / lookup_fast

write to 0xffff88811b430300 of 4 bytes by task 2563 on cpu 0:
 d_make_discardable+0x4f/0x90 fs/dcache.c:1050
 simple_unlink+0x68/0x80 fs/libfs.c:808
 shmem_unlink+0x12d/0x140 mm/shmem.c:3980
 vfs_unlink+0x1c3/0x490 fs/namei.c:5511
 filename_unlinkat+0x1dc/0x410 fs/namei.c:5581
 __do_sys_unlink fs/namei.c:5616 [inline]
 __se_sys_unlink+0x2b/0xe0 fs/namei.c:5613
 __x64_sys_unlink+0x1f/0x30 fs/namei.c:5613
 x64_sys_call+0x2eb6/0x3020 arch/x86/include/generated/asm/syscalls_64.h:88
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811b430300 of 4 bytes by task 2979 on cpu 1:
 d_revalidate fs/namei.c:1034 [inline]
 lookup_fast+0xf1/0x320 fs/namei.c:1868
 walk_component fs/namei.c:2278 [inline]
 lookup_last fs/namei.c:2789 [inline]
 path_lookupat+0x120/0x4c0 fs/namei.c:2813
 filename_lookup+0x18f/0x390 fs/namei.c:2842
 do_readlinkat+0x74/0x2f0 fs/stat.c:571
 __do_sys_readlink fs/stat.c:605 [inline]
 __se_sys_readlink fs/stat.c:602 [inline]
 __x64_sys_readlink+0x47/0x60 fs/stat.c:602
 x64_sys_call+0x2b51/0x3020 arch/x86/include/generated/asm/syscalls_64.h:90
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x08300080 -> 0x00004080

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 2979 Comm: udevd Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
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