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BUG: KCSAN: data-race in __ext4_journal_start_sb / ext4_remount

write to 0xffff888102b84050 of 8 bytes by task 30742 on cpu 1:
 ext4_remount+0x1537/0x1980 fs/ext4/super.c:5995
 legacy_reconfigure+0x8e/0xa0 fs/fs_context.c:633
 reconfigure_super+0x2d3/0x4f0 fs/super.c:906
 do_remount fs/namespace.c:2650 [inline]
 path_mount+0x145a/0x1d20 fs/namespace.c:3310
 do_mount fs/namespace.c:3331 [inline]
 __do_sys_mount fs/namespace.c:3539 [inline]
 __se_sys_mount+0x24b/0x2f0 fs/namespace.c:3516
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3516
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888102b84050 of 8 bytes by task 30744 on cpu 0:
 sb_rdonly include/linux/fs.h:2269 [inline]
 ext4_journal_check_start fs/ext4/ext4_jbd2.c:73 [inline]
 __ext4_journal_start_sb+0x84/0x2d0 fs/ext4/ext4_jbd2.c:98
 __ext4_journal_start fs/ext4/ext4_jbd2.h:326 [inline]
 ext4_da_write_begin+0x3f0/0x7f0 fs/ext4/inode.c:3002
 generic_perform_write+0x1b8/0x3e0 mm/filemap.c:3770
 ext4_buffered_write_iter+0x305/0x400 fs/ext4/file.c:269
 ext4_file_write_iter+0x2e7/0x11f0
 call_write_iter include/linux/fs.h:2163 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x7bc/0x900 fs/read_write.c:594
 ksys_write+0xd9/0x190 fs/read_write.c:647
 __do_sys_write fs/read_write.c:659 [inline]
 __se_sys_write fs/read_write.c:656 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:656
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000000072818000 -> 0x0000000070018000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 30744 Comm: syz-executor.3 Tainted: G        W         5.15.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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