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BUG: KCSAN: data-race in ext4_file_write_iter / ext4_mpage_readpages

write to 0xffff888130e77350 of 8 bytes by task 7395 on cpu 1:
 i_size_write include/linux/fs.h:872 [inline]
 ext4_update_inode_size fs/ext4/ext4.h:3292 [inline]
 ext4_handle_inode_extension fs/ext4/file.c:331 [inline]
 ext4_dio_write_iter fs/ext4/file.c:557 [inline]
 ext4_file_write_iter+0xdff/0x11d0 fs/ext4/file.c:661
 call_write_iter include/linux/fs.h:1977 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
 do_iter_write+0x112/0x4c0 fs/read_write.c:866
 vfs_iter_write+0x4c/0x70 fs/read_write.c:907
 iter_file_splice_write+0x40a/0x750 fs/splice.c:689
 do_splice_from fs/splice.c:767 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:936
 splice_direct_to_actor+0x345/0x650 fs/splice.c:891
 do_splice_direct+0xf5/0x170 fs/splice.c:979
 do_sendfile+0x773/0xda0 fs/read_write.c:1260
 __do_sys_sendfile64 fs/read_write.c:1325 [inline]
 __se_sys_sendfile64 fs/read_write.c:1311 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1311
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888130e77350 of 8 bytes by task 7405 on cpu 0:
 i_size_read include/linux/fs.h:850 [inline]
 ext4_readpage_limit fs/ext4/readpage.c:221 [inline]
 ext4_mpage_readpages+0x34b/0x1130 fs/ext4/readpage.c:265
 ext4_readahead+0x99/0xa0 fs/ext4/inode.c:3262
 read_pages+0x9f/0x530 mm/readahead.c:130
 page_cache_ra_unbounded+0x3a8/0x400 mm/readahead.c:238
 ondemand_readahead+0x56f/0x7a0 mm/readahead.c:267
 page_cache_sync_ra+0x95/0xd0 mm/readahead.c:577
 page_cache_sync_readahead include/linux/pagemap.h:840 [inline]
 filemap_get_pages mm/filemap.c:2381 [inline]
 filemap_read+0x380/0x1210 mm/filemap.c:2464
 generic_file_read_iter+0x84/0x3e0 mm/filemap.c:2615
 ext4_file_read_iter+0x1db/0x290 fs/ext4/file.c:73
 call_read_iter include/linux/fs.h:1971 [inline]
 new_sync_read fs/read_write.c:415 [inline]
 vfs_read+0x565/0x5d0 fs/read_write.c:496
 ksys_read+0xce/0x180 fs/read_write.c:634
 __do_sys_read fs/read_write.c:644 [inline]
 __se_sys_read fs/read_write.c:642 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:642
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 7405 Comm: syz-executor.3 Tainted: G        W         5.12.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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