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BUG: KCSAN: data-race in shmem_get_folio_gfp / shmem_write_end

write to 0xffff888138ef5560 of 8 bytes by task 16932 on cpu 1:
 i_size_write include/linux/fs.h:932 [inline]
 shmem_write_end+0x9a/0x470 mm/shmem.c:2726
 generic_perform_write+0x267/0x410 mm/filemap.c:3929
 shmem_file_write_iter+0xc8/0xe0 mm/shmem.c:2878
 do_iter_write+0x4ad/0x770 fs/read_write.c:860
 vfs_iter_write+0x56/0x70 fs/read_write.c:901
 iter_file_splice_write+0x462/0x7e0 fs/splice.c:736
 do_splice_from fs/splice.c:933 [inline]
 direct_splice_actor+0x8a/0xb0 fs/splice.c:1142
 splice_direct_to_actor+0x31d/0x690 fs/splice.c:1088
 do_splice_direct+0x10d/0x190 fs/splice.c:1194
 do_sendfile+0x3c4/0x980 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:51 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff888138ef5560 of 8 bytes by task 16929 on cpu 0:
 i_size_read include/linux/fs.h:910 [inline]
 shmem_get_folio_gfp+0x13f/0xb40 mm/shmem.c:1958
 shmem_get_folio mm/shmem.c:2119 [inline]
 shmem_file_splice_read+0x198/0x600 mm/shmem.c:2949
 vfs_splice_read fs/splice.c:993 [inline]
 splice_direct_to_actor+0x28c/0x690 fs/splice.c:1069
 do_splice_direct+0x10d/0x190 fs/splice.c:1194
 do_sendfile+0x3c4/0x980 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:51 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

value changed: 0x0000000000006640 -> 0x000000000000664c

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 16929 Comm: syz-executor.4 Tainted: G        W          6.7.0-rc4-syzkaller-00009-gbee0e7762ad2 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
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