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BUG: KCSAN: data-race in shmem_getpage_gfp / shmem_write_end

write to 0xffff8881398f0120 of 8 bytes by task 7804 on cpu 0:
 i_size_write include/linux/fs.h:886 [inline]
 shmem_write_end+0x59/0x380 mm/shmem.c:2535
 generic_perform_write+0x264/0x3f0 mm/filemap.c:3749
 __generic_file_write_iter+0xe3/0x280 mm/filemap.c:3866
 generic_file_write_iter+0x79/0x1c0 mm/filemap.c:3898
 do_iter_write+0x494/0x750 fs/read_write.c:855
 vfs_writev fs/read_write.c:928 [inline]
 do_pwritev+0x235/0x430 fs/read_write.c:1025
 __do_sys_pwritev fs/read_write.c:1072 [inline]
 __se_sys_pwritev fs/read_write.c:1067 [inline]
 __x64_sys_pwritev+0x54/0x60 fs/read_write.c:1067
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffff8881398f0120 of 8 bytes by task 36 on cpu 1:
 i_size_read include/linux/fs.h:864 [inline]
 shmem_getpage_gfp+0x1a3/0x1750 mm/shmem.c:1854
 shmem_getpage mm/shmem.c:150 [inline]
 shmem_file_read_iter+0x161/0x6c0 mm/shmem.c:2592
 do_iter_read+0x492/0x760 fs/read_write.c:790
 vfs_iter_read+0x4c/0x70 fs/read_write.c:832
 lo_read_simple drivers/block/loop.c:290 [inline]
 do_req_filebacked drivers/block/loop.c:500 [inline]
 loop_handle_cmd drivers/block/loop.c:1864 [inline]
 loop_process_work+0x783/0x1340 drivers/block/loop.c:1899
 loop_workfn+0x2d/0x40 drivers/block/loop.c:1923
 process_one_work+0x3d3/0x720 kernel/workqueue.c:2289
 worker_thread+0x618/0xa70 kernel/workqueue.c:2436
 kthread+0x1a9/0x1e0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30

value changed: 0x00000000005dd000 -> 0x00000000005e1000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 36 Comm: kworker/u4:2 Not tainted 6.0.0-rc6-syzkaller-00286-ga63f2e7cb110-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2022
Workqueue: loop5 loop_workfn
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