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

[Greg Kroah-Hartman]

On Mon, Dec 16, 2019 at 10:18:48AM +0100, Andre Tomt wrote:
> 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.
> 

Great!

Thanks Jack for finding the fix and Andre for reporting this.  I'll go
queue this fix up right now.

greg k-h