Re: [PATCH 4.19 153/306] block: fix the DISCARD request merge (4.19.87+ crash)

[Andre Tomt]

On 16.12.2019 08:42, Jack Wang wrote:
> Andre Tomt <andre@xxxxxxxx> ä2019å12æ14æåå äå3:24åéï
> > 4.19.87, 4.19.88, 4.19.89 all lock up frequently on some of my systems.
> > The same systems run 5.4.3 fine, so the newer trees are probably OK.
> > Reverting this commit on top of 4.19.87 makes everything stable.
> >
> > To trigger it all I have to do is re-rsyncing a directory tree with some
> > changed files churn, it will usually crash in 10 to 30 minutes.
> >
> > The systems crashing has ext4 filesystem on a two ssd md raid1 mounted
> > with the mount option discard. If mounting it without discard, the
> > crashes no longer seem to occur.
> >
> > No oops/panic made it to the ipmi console. I suspect the console is just
> > misbehaving and it didnt really livelock. At one point one line of the
> > crash made it to the console (kernel BUG at block/blk-core.c:1776), and
> > it was enough to pinpoint this commit. Note that the line number might
> > be off, as I was attempting a bisect at the time.
> >
> > This commit also made it to 4.14.x, but I have not tested it.
> Hi Andre,
>
> I noticed one fix is missing for discard merge in 4.19.y
> 2a5cf35cd6c5 ("block: fix single range discard merge")
>
> Can you try if it helps? just "git cherry-pick 2a5cf35cd6c5"

Indeed, adding this commit on top a clean 4.19.89 fixes the issue. So 
far survived about an hour of rsyncing file churn.