syzbot

==================================================================
BUG: KCSAN: data-race in _copy_to_iter / copy_page_from_iter_atomic

write to 0xffff88811d91b440 of 3008 bytes by task 10463 on cpu 1:
 instrument_copy_from_user_before include/linux/instrumented.h:130 [inline]
 copy_from_user_iter lib/iov_iter.c:54 [inline]
 iterate_ubuf include/linux/iov_iter.h:30 [inline]
 iterate_and_advance2 include/linux/iov_iter.h:300 [inline]
 iterate_and_advance include/linux/iov_iter.h:328 [inline]
 __copy_from_iter lib/iov_iter.c:249 [inline]
 copy_page_from_iter_atomic+0x294/0xfa0 lib/iov_iter.c:483
 copy_folio_from_iter_atomic include/linux/uio.h:210 [inline]
 generic_perform_write+0x2d2/0x4b0 mm/filemap.c:4132
 shmem_file_write_iter+0xc2/0xe0 mm/shmem.c:3477
 new_sync_write fs/read_write.c:591 [inline]
 vfs_write+0x79b/0x950 fs/read_write.c:684
 ksys_write+0xeb/0x1b0 fs/read_write.c:736
 __do_sys_write fs/read_write.c:747 [inline]
 __se_sys_write fs/read_write.c:744 [inline]
 __x64_sys_write+0x42/0x50 fs/read_write.c:744
 x64_sys_call+0x2a45/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811d91b000 of 4096 bytes by task 10467 on cpu 0:
 instrument_copy_to_user include/linux/instrumented.h:113 [inline]
 copy_to_user_iter lib/iov_iter.c:24 [inline]
 iterate_ubuf include/linux/iov_iter.h:30 [inline]
 iterate_and_advance2 include/linux/iov_iter.h:300 [inline]
 iterate_and_advance include/linux/iov_iter.h:328 [inline]
 _copy_to_iter+0x133/0xd10 lib/iov_iter.c:185
 copy_page_to_iter+0x171/0x2b0 lib/iov_iter.c:362
 copy_folio_to_iter include/linux/uio.h:198 [inline]
 shmem_file_read_iter+0x2c3/0x540 mm/shmem.c:3425
 new_sync_read fs/read_write.c:489 [inline]
 vfs_read+0x5e6/0x710 fs/read_write.c:570
 ksys_read+0xeb/0x1b0 fs/read_write.c:713
 __do_sys_read fs/read_write.c:722 [inline]
 __se_sys_read fs/read_write.c:720 [inline]
 __x64_sys_read+0x42/0x50 fs/read_write.c:720
 x64_sys_call+0x2a3b/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:1
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 10467 Comm: syz.0.2308 Not tainted 6.14.0-syzkaller-09584-g7d06015d936c #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
==================================================================