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BUG: KCSAN: data-race in shmem_file_read_iter / shmem_write_end

write to 0xffff88813d54b5b0 of 8 bytes by task 9741 on cpu 0:
 i_size_write include/linux/fs.h:934 [inline]
 shmem_write_end+0x9a/0x470 mm/shmem.c:2741
 generic_perform_write+0x267/0x410 mm/filemap.c:3941
 shmem_file_write_iter+0xc8/0xe0 mm/shmem.c:2893
 call_write_iter include/linux/fs.h:2087 [inline]
 new_sync_write fs/read_write.c:497 [inline]
 vfs_write+0x760/0x8d0 fs/read_write.c:590
 ksys_write+0xeb/0x1a0 fs/read_write.c:643
 __do_sys_write fs/read_write.c:655 [inline]
 __se_sys_write fs/read_write.c:652 [inline]
 __x64_sys_write+0x42/0x50 fs/read_write.c:652
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff88813d54b5b0 of 8 bytes by task 6696 on cpu 1:
 i_size_read include/linux/fs.h:912 [inline]
 shmem_file_read_iter+0x96/0x550 mm/shmem.c:2777
 call_read_iter include/linux/fs.h:2081 [inline]
 new_sync_read fs/read_write.c:395 [inline]
 vfs_read+0x5ab/0x6a0 fs/read_write.c:476
 ksys_read+0xeb/0x1a0 fs/read_write.c:619
 __do_sys_read fs/read_write.c:629 [inline]
 __se_sys_read fs/read_write.c:627 [inline]
 __x64_sys_read+0x42/0x50 fs/read_write.c:627
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

value changed: 0x00000000002f3000 -> 0x00000000002f6000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 6696 Comm: udevd Not tainted 6.8.0-rc5-syzkaller-00278-g603c04e27c3e #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
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