syzbot

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BUG: KCSAN: data-race in shmem_file_read_iter / shmem_write_end

write to 0xffff888143f910d8 of 8 bytes by task 24845 on cpu 0:
 i_size_write include/linux/fs.h:905 [inline]
 shmem_write_end+0x9a/0x4a0 mm/shmem.c:2598
 generic_perform_write+0x253/0x3d0 mm/filemap.c:3934
 __generic_file_write_iter+0xe6/0x290 mm/filemap.c:4051
 generic_file_write_iter+0x7d/0x1c0 mm/filemap.c:4083
 do_iter_write+0x4ae/0x770 fs/read_write.c:860
 vfs_iter_write+0x50/0x70 fs/read_write.c:901
 iter_file_splice_write+0x456/0x7d0 fs/splice.c:795
 do_splice_from fs/splice.c:873 [inline]
 direct_splice_actor+0x84/0xa0 fs/splice.c:1039
 splice_direct_to_actor+0x2ee/0x5f0 fs/splice.c:994
 do_splice_direct+0x104/0x180 fs/splice.c:1082
 do_sendfile+0x3b8/0x950 fs/read_write.c:1254
 __do_sys_sendfile64 fs/read_write.c:1316 [inline]
 __se_sys_sendfile64 fs/read_write.c:1308 [inline]
 __x64_sys_sendfile64+0xbd/0x150 fs/read_write.c:1308
 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 0xffff888143f910d8 of 8 bytes by task 24844 on cpu 1:
 i_size_read include/linux/fs.h:883 [inline]
 shmem_file_read_iter+0x406/0x560 mm/shmem.c:2634
 call_read_iter include/linux/fs.h:1862 [inline]
 generic_file_splice_read+0xe3/0x290 fs/splice.c:419
 do_splice_to fs/splice.c:902 [inline]
 splice_direct_to_actor+0x25a/0x5f0 fs/splice.c:973
 do_splice_direct+0x104/0x180 fs/splice.c:1082
 do_sendfile+0x3b8/0x950 fs/read_write.c:1254
 __do_sys_sendfile64 fs/read_write.c:1316 [inline]
 __se_sys_sendfile64 fs/read_write.c:1308 [inline]
 __x64_sys_sendfile64+0xbd/0x150 fs/read_write.c:1308
 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

value changed: 0x0000000000005d3e -> 0x0000000000005dac

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 24844 Comm: syz-executor.5 Not tainted 6.4.0-rc5-syzkaller-00002-gf8dba31b0a82 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/25/2023
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