Re: [4/4] rhashtable: improve rhashtable_walk stability when stop/start used.

[NeilBrown]

On Thu, Jul 05 2018, Paolo Abeni wrote:

>
> While testing new code that uses the rhashtable walker, I'm obeserving
> an use after free, that is apparently caused by the above:
>
> [  146.834815] ==================================================================
> [  146.842933] BUG: KASAN: use-after-free in inet_frag_worker+0x9f/0x210
                                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^

Hi,
 did you get a chance to run ./scripts/faddr2line on this address and
find out where it is crashing?  I had a look in the code you posted and
couldn't see anything obvious.


> [  146.850120] Read of size 4 at addr ffff881b6b9342d8 by task kworker/13:1/177
> [  146.857984] 
> [  146.859645] CPU: 13 PID: 177 Comm: kworker/13:1 Not tainted 4.18.0-rc3.mirror_unclone_6_frag_dbg+ #1974
> [  146.870128] Hardware name: Dell Inc. PowerEdge R730/072T6D, BIOS 2.1.7 06/16/2016
> [  146.878478] Workqueue: events inet_frag_worker
> [  146.883433] Call Trace:
> [  146.886162]  dump_stack+0x90/0xe3
> [  146.889861]  print_address_description+0x6a/0x2a0
> [  146.895109]  kasan_report+0x176/0x2d0
> [  146.899193]  ? inet_frag_worker+0x9f/0x210
> [  146.903762]  inet_frag_worker+0x9f/0x210
> [  146.908142]  process_one_work+0x24f/0x6e0
> [  146.912614]  ? process_one_work+0x1a6/0x6e0
> [  146.917285]  worker_thread+0x4e/0x3d0
> [  146.921373]  kthread+0x106/0x140
> [  146.924970]  ? process_one_work+0x6e0/0x6e0
> [  146.929637]  ? kthread_bind+0x10/0x10
> [  146.933723]  ret_from_fork+0x3a/0x50
> [  146.937717] 
> [  146.939377] Allocated by task 177:
> [  146.943170]  kasan_kmalloc+0x86/0xb0
> [  146.947158]  __kmalloc_node+0x181/0x430
> [  146.951438]  kvmalloc_node+0x4f/0x70
> [  146.955427]  alloc_bucket_spinlocks+0x34/0xa0

This seems to suggest that it is one of the bucket spinlocks that is
being incorrectly referenced, but they aren't referenced in the failing
code at all.  I cannot imagine how to interpret that.

Thanks,
NeilBrown

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