BUG: KCSAN: data-race in __pagevec_lru_add_fn / __zerocopy_sg_from_iter

write to 0xffffea00051a3948 of 8 bytes by task 1568 on cpu 0:
 __list_add include/linux/list.h:71 [inline]
 list_add include/linux/list.h:86 [inline]
 add_page_to_lru_list include/linux/mm_inline.h:88 [inline]
 __pagevec_lru_add_fn+0x38c/0x490 mm/swap.c:1043
 __pagevec_lru_add+0x189/0x240 mm/swap.c:1061
 lru_cache_add+0x121/0x150 mm/swap.c:475
 add_to_page_cache_lru+0x150/0x1b0 mm/filemap.c:983
 pagecache_get_page+0x6a3/0x900 mm/filemap.c:1896
 grab_cache_page_write_begin+0x3f/0x70 mm/filemap.c:3610
 ext4_da_write_begin+0x305/0x820 fs/ext4/inode.c:2984
 generic_perform_write+0x196/0x3c0 mm/filemap.c:3656
 ext4_buffered_write_iter+0x2f2/0x3f0 fs/ext4/file.c:269
 ext4_file_write_iter+0x2e7/0x11d0 fs/ext4/file.c:519
 call_write_iter include/linux/fs.h:2114 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x69d/0x770 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffffea00051a3948 of 8 bytes by task 1578 on cpu 1:
 page_is_pfmemalloc include/linux/mm.h:1678 [inline]
 __skb_fill_page_desc include/linux/skbuff.h:2184 [inline]
 skb_fill_page_desc include/linux/skbuff.h:2205 [inline]
 __zerocopy_sg_from_iter+0x658/0x820 net/core/datagram.c:680
 skb_zerocopy_iter_stream+0xfe/0x360 net/core/skbuff.c:1347
 tcp_sendmsg_locked+0xb6c/0x24b0 net/ipv4/tcp.c:1381
 tcp_sendmsg+0x2c/0x40 net/ipv4/tcp.c:1461
 inet_sendmsg+0x5f/0x80 net/ipv4/af_inet.c:821
 sock_sendmsg_nosec net/socket.c:703 [inline]
 sock_sendmsg net/socket.c:723 [inline]
 ____sys_sendmsg+0x360/0x4d0 net/socket.c:2392
 ___sys_sendmsg net/socket.c:2446 [inline]
 __sys_sendmmsg+0x315/0x4b0 net/socket.c:2532
 __do_sys_sendmmsg net/socket.c:2561 [inline]
 __se_sys_sendmmsg net/socket.c:2558 [inline]
 __x64_sys_sendmmsg+0x53/0x60 net/socket.c:2558
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000000000000000 -> 0xffffea00051a3908

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1578 Comm: syz-executor.1 Not tainted 5.14.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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