linux-kernel - Re: [PATCH v6 08/71] Maple Tree: Add new data structure

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Date:   Wed, 2 Mar 2022 14:08:06 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     Vasily Gorbik <gor@...ux.ibm.com>
CC:     "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>
Subject: Re: [PATCH v6 08/71] Maple Tree: Add new data structure



* Vasily Gorbik <gor@...ux.ibm.com> [220301 17:51]:
> On Tue, Mar 01, 2022 at 08:39:44PM +0000, Liam Howlett wrote:
> > * Vasily Gorbik <gor@...ux.ibm.com> [220228 21:01]:
> > > This condition is not present in mas_dead_leaves() where we potentially
> > > iterate over all 16 slots, simply checking that we have a "valid" node pointer
> > > with:
> > > 
> > > entry & ~MAPLE_NODE_MASK != 0
> > 
> > I have fixed this and another issue that Hugh pointed out [1].  I have
> > been working on an s390 VM since you reported your issue and have been
> > getting strange behaviour and have been able to detect the bug reported
> > by Hugh with the config KASAN option.  With the fix I described above
> > and fixing the do_mas_align_munmap() splitting order I broken in my
> > linked list removal, I am now able to boot my s390 VM and log in with
> > KASAN, VM debug, maple tree debug, rbtree debug, debug page flags, and
> > Poison pages after freeing all set in the config I use.  I've pushed the
> > fix to a tag on my branch [2] and I'd appreciate it if you could test it
> > on your side.
> 
> Great, I gave it a spin and it looks much better now! I'll go run some stress
> tests.
> 
> BTW, since you've made efforts to isolate mapple tests in userspace I
> wonder how much sense it would make to use libfuzzer to give API some good
> coverage-guided exercise.
> 
> I've written a minimal libfuzzer test (just a hack) for the "Normal API" and got
> couple of flavours of crashes. Just rebased onto your latest branch state
> and still get them. Please have a look if those are valid findings.


Thanks!  Yes, the first one is certainly a valid bug.  I was able to
reproduce it and fix the issue in my tree.  I'll have a look and see
what else it throws out.

Cheers,
Liam