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BUG: KCSAN: data-race in ext4_journal_check_start / ext4_remount

read to 0xffff888218648850 of 8 bytes by task 9047 on cpu 0:
 ext4_journal_check_start+0x65/0x150 fs/ext4/ext4_jbd2.c:51
 __ext4_journal_start_sb+0x5f/0x250 fs/ext4/ext4_jbd2.c:76
 __ext4_journal_start fs/ext4/ext4_jbd2.h:325 [inline]
 ext4_da_write_begin+0x35d/0x840 fs/ext4/inode.c:2977
 generic_perform_write+0x136/0x320 mm/filemap.c:3309
 ext4_buffered_write_iter+0x143/0x290 fs/ext4/file.c:252
 ext4_file_write_iter+0xf4/0xd40 fs/ext4/file.c:547
 call_write_iter include/linux/fs.h:1902 [inline]
 new_sync_write+0x388/0x4a0 fs/read_write.c:483
 __vfs_write+0xb1/0xc0 fs/read_write.c:496
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x18a/0x390 fs/read_write.c:542
 ksys_write+0xd5/0x1b0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x4c/0x60 fs/read_write.c:620
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff888218648850 of 8 bytes by task 9057 on cpu 1:
 ext4_remount+0x685/0x13a0 fs/ext4/super.c:5361
 legacy_reconfigure+0x9a/0xc0 fs/fs_context.c:670
 reconfigure_super+0x36a/0x570 fs/super.c:955
 do_remount fs/namespace.c:2553 [inline]
 do_mount+0x1136/0x14f0 fs/namespace.c:3133
 ksys_mount+0xe8/0x160 fs/namespace.c:3351
 __do_sys_mount fs/namespace.c:3365 [inline]
 __se_sys_mount fs/namespace.c:3362 [inline]
 __x64_sys_mount+0x70/0x90 fs/namespace.c:3362
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 9057 Comm: syz-executor.2 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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