Ben, The patch is symptomatic. fq_tin_dequeue() already checks if the list is empty before it tries to access first entry. I see no point in using the _or_null() + WARN_ON. The 0x3c deref is likely an offset off of NULL base pointer. Did you check gdb/addr2line of the ieee80211_tx_dequeue+0xfb? Where did it point to? I suspect there's not enough synchronization between quescing the device/ath10k after fw crashes and performing mac80211's reconfig procedure. Michał On 8 June 2018 at 23:40, Arend van Spriel <arend.vanspriel@xxxxxxxxxxxx> wrote: > On 6/8/2018 5:17 PM, Ben Greear wrote: > > I recalled an email from Michał leaving tieto so adding his alternate email > he provided back then. > > Gr. AvS > > >> On 06/07/2018 04:59 PM, Cong Wang wrote: >>> >>> On Thu, Jun 7, 2018 at 4:48 PM, <greearb@xxxxxxxxxxxxxxx> wrote: >>>> >>>> diff --git a/include/net/fq_impl.h b/include/net/fq_impl.h >>>> index be7c0fa..cb911f0 100644 >>>> --- a/include/net/fq_impl.h >>>> +++ b/include/net/fq_impl.h >>>> @@ -78,7 +78,10 @@ static struct sk_buff *fq_tin_dequeue(struct fq *fq, >>>> return NULL; >>>> } >>>> >>>> - flow = list_first_entry(head, struct fq_flow, flowchain); >>>> + flow = list_first_entry_or_null(head, struct fq_flow, >>>> flowchain); >>>> + >>>> + if (WARN_ON_ONCE(!flow)) >>>> + return NULL; >>> >>> >>> This does not make sense either. list_first_entry_or_null() >>> returns NULL only when the list is empty, but we already check >>> list_empty() right before this code, and it is protected by fq->lock. >>> >> >> Hello Michal, >> >> git blame shows you as the author of the fq_impl.h code. >> >> I saw a crash when debugging funky ath10k firmware in a 4.16 + hacks >> kernel. There was an apparent >> mostly-null deref in the fq_tin_dequeue method. According to gdb, it >> was within >> 1 line of the dereference of 'flow'. >> >> My hack above is probably not that useful. Cong thinks maybe the >> locking is bad. >> >> If you get a chance, please review this thread and see if you have any >> ideas for >> a better fix (or better debugging code). >> >> As always, if you would like me to generate you a buggy firmware that >> will crash >> in the tx path and cause all sorts of mayhem in the ath10k driver and >> wifi stack, >> I will be happy to do so. >> >> https://www.mail-archive.com/netdev@xxxxxxxxxxxxxxx/msg239738.html >> >> Thanks, >> Ben >> >
