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Date:   Tue, 07 Aug 2018 20:42:18 +0000
From:   bugzilla-daemon@...zilla.kernel.org
To:     linux-ext4@...nel.org
Subject: [Bug 200753] write I/O error for inode structure leads to operation
 failure without any warning or error

https://bugzilla.kernel.org/show_bug.cgi?id=200753

--- Comment #17 from Theodore Tso (tytso@....edu) ---
I see your problem.   Your dm-io.c is broken:

                        printk(KERN_INFO "WRITE block = %lu
",bio->bi_iter.bi_sector / 8);
                        bno = bio->bi_iter.bi_sector / 8;       
                        if( mdt->error && bno == mdt->errorBlockNumber &&
mdt->mode != 'R') {
                                printk("WRITE ERROR!!\n");
                                printk(KERN_INFO "%s():ERROR ON block =
%lu\n",__func__,(bio->bi_iter.bi_sector / 8) - 1);
                                bio_endio(bio);
                                // bio_io_error(bio);
                                return DM_MAPIO_SUBMITTED;

It wasn't actually return an error to file system!

Once I fixed your dm-io, I confirmed that errors to the journal do in fact
cause a jbd2 error to be logged in dmesg:

[18995.919032] WRITE ERROR!!
[18995.919039] io_map():ERROR ON block = 196609
[18995.919251] Aborting journal on device dm-18-8.
[18995.919278] WRITE block = 196608 
[18998.747065] READ block = 204 
[18998.747258] WRITE block = 0 
[18998.748982] EXT4-fs error (device dm-18): ext4_journal_check_start:61:
Detected aborted journal
[18998.749199] EXT4-fs (dm-18): Remounting filesystem read-only

Given your assertion that write errors to the journal don't cause the kernel to
complain, and I have just demonstrated that errors to the journal *do* cause
the kernel to complain, the reliability of your other observations are
seriously called into question.   Combined with your fundamental
misunderstandings of how file systems work (including how buffered writes work,
and how symlinks work), I'm going to gently suggest that you spend some time
gathering a much deeper understanding of how kernel storage works before you
waste more kernel developers time....

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