linux-kernel - Re: [PATCH v1 01/25] net: core: device_rename: Use rwsem instead of a seqcount

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200519161141.5fbab730@hermes.lan>
Date:   Tue, 19 May 2020 16:11:41 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        "Sebastian A. Siewior" <bigeasy@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH v1 01/25] net: core: device_rename: Use rwsem instead of
 a seqcount

On Wed, 20 May 2020 00:23:48 +0200
Thomas Gleixner <tglx@...utronix.de> wrote:

> Stephen Hemminger <stephen@...workplumber.org> writes:
> > On Tue, 19 May 2020 23:45:23 +0200
> > "Ahmed S. Darwish" <a.darwish@...utronix.de> wrote:
> >  
> >> Sequence counters write paths are critical sections that must never be
> >> preempted, and blocking, even for CONFIG_PREEMPTION=n, is not allowed.
> >> 
> >> Commit 5dbe7c178d3f ("net: fix kernel deadlock with interface rename and
> >> netdev name retrieval.") handled a deadlock, observed with
> >> CONFIG_PREEMPTION=n, where the devnet_rename seqcount read side was
> >> infinitely spinning: it got scheduled after the seqcount write side
> >> blocked inside its own critical section.
> >> 
> >> To fix that deadlock, among other issues, the commit added a
> >> cond_resched() inside the read side section. While this will get the
> >> non-preemptible kernel eventually unstuck, the seqcount reader is fully
> >> exhausting its slice just spinning -- until TIF_NEED_RESCHED is set.
> >> 
> >> The fix is also still broken: if the seqcount reader belongs to a
> >> real-time scheduling policy, it can spin forever and the kernel will
> >> livelock.
> >> 
> >> Disabling preemption over the seqcount write side critical section will
> >> not work: inside it are a number of GFP_KERNEL allocations and mutex
> >> locking through the drivers/base/ :: device_rename() call chain.
> >> 
> >> From all the above, replace the seqcount with a rwsem.
> >> 
> >> Fixes: 5dbe7c178d3f (net: fix kernel deadlock with interface rename and netdev name retrieval.)
> >> Fixes: 30e6c9fa93cf (net: devnet_rename_seq should be a seqcount)
> >> Fixes: c91f6df2db49 (sockopt: Change getsockopt() of SO_BINDTODEVICE to return an interface name)
> >> Cc: <stable@...r.kernel.org>
> >> Signed-off-by: Ahmed S. Darwish <a.darwish@...utronix.de>
> >> Reviewed-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>  
> >
> > Have your performance tested this with 1000's of network devices?  
> 
> No. We did not. -ENOTESTCASE

Please try, it isn't that hard..

# time for ((i=0;i<1000;i++)); do ip li add dev dummy$i type dummy; done

real	0m17.002s
user	0m1.064s
sys	0m0.375s