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BUG: KCSAN: data-race in ext4_mark_iloc_dirty / generic_update_time

write to 0xffff888125703b80 of 16 bytes by task 10855 on cpu 1:
 generic_update_time+0x5c/0x270 fs/inode.c:1654
 update_time fs/inode.c:1683 [inline]
 touch_atime+0x172/0x190 fs/inode.c:1754
 file_accessed include/linux/fs.h:2202 [inline]
 generic_file_buffered_read mm/filemap.c:2258 [inline]
 generic_file_read_iter+0x116e/0x1440 mm/filemap.c:2324
 ext4_file_read_iter fs/ext4/file.c:77 [inline]
 ext4_file_read_iter+0xfa/0x240 fs/ext4/file.c:65
 call_read_iter include/linux/fs.h:1889 [inline]
 generic_file_splice_read+0x35c/0x500 fs/splice.c:307
 do_splice_to+0xf2/0x130 fs/splice.c:877
 splice_direct_to_actor+0x1a1/0x510 fs/splice.c:954
 do_splice_direct+0x161/0x1e0 fs/splice.c:1063
 do_sendfile+0x384/0x7f0 fs/read_write.c:1464
 __do_sys_sendfile64 fs/read_write.c:1525 [inline]
 __se_sys_sendfile64 fs/read_write.c:1511 [inline]
 __x64_sys_sendfile64+0x12a/0x140 fs/read_write.c:1511
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888125703b80 of 8 bytes by task 10833 on cpu 0:
 ext4_do_update_inode fs/ext4/inode.c:5266 [inline]
 ext4_mark_iloc_dirty+0x4e5/0x1580 fs/ext4/inode.c:5876
 ext4_mark_inode_dirty+0xe9/0x420 fs/ext4/inode.c:6055
 ext4_dirty_inode+0x86/0xb0 fs/ext4/inode.c:6086
 __mark_inode_dirty+0x5d4/0x940 fs/fs-writeback.c:2258
 mark_inode_dirty include/linux/fs.h:2165 [inline]
 ext4_setattr+0xbeb/0x15a0 fs/ext4/inode.c:5675
 notify_change+0x7e1/0xaa0 fs/attr.c:337
 do_truncate+0xfb/0x180 fs/open.c:64
 do_sys_ftruncate+0x30f/0x340 fs/open.c:195
 __do_sys_ftruncate fs/open.c:205 [inline]
 __se_sys_ftruncate fs/open.c:203 [inline]
 __x64_sys_ftruncate+0x3f/0x50 fs/open.c:203
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 10833 Comm: syz-executor.5 Not tainted 5.4.0-rc7+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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