[Bug 201685] ext4 file system corruption

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=201685

--- Comment #263 from Rainer Fiebig (jrf@mailbox.org) ---
(In reply to Guenter Roeck from comment #240)
> As mentioned earlier, I only ever saw the problem on two of four systems
> (see #57), all running the same kernel and the same version of Ubuntu. The
> only differences are mainboard, CPU, and attached drive types.
> 
> I don't think we know for sure what it takes to trigger the problem. We have
> seen various guesses, from gcc version to l1tf mitigation to CPU type,
> broken hard drives, and whatnot. At this time evidence points to the block
> subsystem, with bisect pointing to a commit which relies on the state of the
> HW queue (empty or not) in conjunction with the 'none' io scheduler. This
> may suggest that drive speed and access timing may be involved. That guess
> may of course be just as wrong as all the others.
> 
> Let's just hope that Jens will be able to track down and fix the problem.
> Then we may be able to get a better idea what it actually takes to trigger
> it.

It would indeed be nice to get a short summary *here* of what happened and why,
once the dust has settled.

It would also be interesting to know why all the testing in the run-up to 4.19
didn't catch it, including rc-kernels. It's imo for instance unlikely that
everybody just tested with CONFIG_SCSI_MQ_DEFAULT=n.

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