kernel null pointer at nvme_tcp_init_iter+0x7d/0xd0 [nvme_tcp]

[Ming Lei]

On Mon, Feb 08, 2021 at 11:21:53PM -0800, Sagi Grimberg wrote:
> 
> 
> On 2/8/21 8:21 PM, Ming Lei wrote:
> > On Mon, Feb 08, 2021 at 10:42:28AM -0800, Sagi Grimberg wrote:
> > > 
> > > > > Hi Sagi
> > > > > 
> > > > > On 2/8/21 5:46 PM, Sagi Grimberg wrote:
> > > > > > 
> > > > > > > Hello
> > > > > > > 
> > > > > > > We found this kernel NULL pointer issue with latest
> > > > > > > linux-block/for-next and it's 100% reproduced, let me know
> > > > > > > if you need more info/testing, thanks
> > > > > > > 
> > > > > > > Kernel repo:
> > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git
> > > > > > > Commit: 11f8b6fd0db9 - Merge branch 'for-5.12/io_uring' into for-next
> > > > > > > 
> > > > > > > Reproducer: blktests nvme-tcp/012
> > > > > > 
> > > > > > Thanks for reporting Ming, I've tried to reproduce this on my VM
> > > > > > but did not succeed. Given that you have it 100% reproducible,
> > > > > > can you try to revert commit:
> > > > > > 
> > > > > > 0dc9edaf80ea nvme-tcp: pass multipage bvec to request iov_iter
> > > > > > 
> > > > > 
> > > > > Revert this commit fixed the issue and I've attached the config. :)
> > > > 
> > > > Good to know,
> > > > 
> > > > I see some differences that I should probably change to hit this:
> > > > -- 
> > > > @@ -254,14 +256,15 @@ CONFIG_PERF_EVENTS=y
> > > >    # end of Kernel Performance Events And Counters
> > > > 
> > > >    CONFIG_VM_EVENT_COUNTERS=y
> > > > +CONFIG_SLUB_DEBUG=y
> > > >    # CONFIG_COMPAT_BRK is not set
> > > > -CONFIG_SLAB=y
> > > > -# CONFIG_SLUB is not set
> > > > -# CONFIG_SLOB is not set
> > > > -CONFIG_SLAB_MERGE_DEFAULT=y
> > > > -# CONFIG_SLAB_FREELIST_RANDOM is not set
> > > > +# CONFIG_SLAB is not set
> > > > +CONFIG_SLUB=y
> > > > +# CONFIG_SLAB_MERGE_DEFAULT is not set
> > > > +CONFIG_SLAB_FREELIST_RANDOM=y
> > > >    # CONFIG_SLAB_FREELIST_HARDENED is not set
> > > > -# CONFIG_SHUFFLE_PAGE_ALLOCATOR is not set
> > > > +CONFIG_SHUFFLE_PAGE_ALLOCATOR=y
> > > > +CONFIG_SLUB_CPU_PARTIAL=y
> > > >    CONFIG_SYSTEM_DATA_VERIFICATION=y
> > > >    CONFIG_PROFILING=y
> > > >    CONFIG_TRACEPOINTS=y
> > > > @@ -299,7 +302,8 @@ CONFIG_HAVE_INTEL_TXT=y
> > > >    CONFIG_X86_64_SMP=y
> > > >    CONFIG_ARCH_SUPPORTS_UPROBES=y
> > > >    CONFIG_FIX_EARLYCON_MEM=y
> > > > -CONFIG_PGTABLE_LEVELS=4
> > > > +CONFIG_DYNAMIC_PHYSICAL_MASK=y
> > > > +CONFIG_PGTABLE_LEVELS=5
> > > >    CONFIG_CC_HAS_SANE_STACKPROTECTOR=y
> > > > -- 
> > > > 
> > > > Probably CONFIG_SLUB and CONFIG_SLUB_DEBUG should be used.
> > > 
> > > Used your profile and this still does not happen :(
> > 
> > One obvious error is that nr_segments is computed wrong.
> > 
> > Yi, can you try the following patch?
> > 
> > diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
> > index 881d28eb15e9..a393d99b74e1 100644
> > --- a/drivers/nvme/host/tcp.c
> > +++ b/drivers/nvme/host/tcp.c
> > @@ -239,9 +239,14 @@ static void nvme_tcp_init_iter(struct nvme_tcp_request *req,
> >   		offset = 0;
> >   	} else {
> >   		struct bio *bio = req->curr_bio;
> > +		struct bio_vec bv;
> > +		struct bvec_iter iter;
> > +
> > +		nsegs = 0;
> > +		bio_for_each_bvec(bv, bio, iter)
> > +			nsegs++;
> >   		vec = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
> > -		nsegs = bio_segments(bio);
> 
> This was exactly the patch that caused the issue.

What was the issue you are talking about? Any link or commit hash?

nvme-tcp builds iov_iter(BVEC) from __bvec_iter_bvec(), the segment
number has to be the actual bvec number. But bio_segment() just returns
number of the single-page segment, which is wrong for iov_iter.

Please see the same usage in lo_rw_aio().

-- 
Ming