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
| ||
|
Message-ID: <CANn89iJMbMZdnJRP0CUVfEi20whhShBfO+DAmdaerhiXfiTx5A@mail.gmail.com> Date: Fri, 1 Dec 2023 10:10:03 +0100 From: Eric Dumazet <edumazet@...gle.com> To: Judy Hsiao <judyhsiao@...omium.org> Cc: David Ahern <dsahern@...nel.org>, Simon Horman <horms@...nel.org>, Douglas Anderson <dianders@...omium.org>, Brian Haley <haleyb.dev@...il.com>, "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Joel Granados <joel.granados@...il.com>, Julian Anastasov <ja@....bg>, Leon Romanovsky <leon@...nel.org>, Luis Chamberlain <mcgrof@...nel.org>, Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org, netdev@...r.kernel.org Subject: Re: [PATCH v1] neighbour: Don't let neigh_forced_gc() disable preemption for long On Fri, Dec 1, 2023 at 9:39 AM Judy Hsiao <judyhsiao@...omium.org> wrote: > > We are seeing cases where neigh_cleanup_and_release() is called by > neigh_forced_gc() many times in a row with preemption turned off. > When running on a low powered CPU at a low CPU frequency, this has > been measured to keep preemption off for ~10 ms. That's not great on a > system with HZ=1000 which expects tasks to be able to schedule in > with ~1ms latency. This will not work in general, because this code runs with BH blocked. jiffies will stay untouched for many more ms on systems with only one CPU. I would rather not rely on jiffies here but ktime_get_ns() [1] Also if we break the loop based on time, we might be unable to purge the last elements in gc_list. We might need to use a second list to make sure to cycle over all elements eventually. [1] diff --git a/net/core/neighbour.c b/net/core/neighbour.c index df81c1f0a57047e176b7c7e4809d2dae59ba6be5..e2340e6b07735db8cf6e75d23ef09bb4b0db53b4 100644 --- a/net/core/neighbour.c +++ b/net/core/neighbour.c @@ -253,9 +253,11 @@ static int neigh_forced_gc(struct neigh_table *tbl) { int max_clean = atomic_read(&tbl->gc_entries) - READ_ONCE(tbl->gc_thresh2); + u64 tmax = ktime_get_ns() + NSEC_PER_MSEC; unsigned long tref = jiffies - 5 * HZ; struct neighbour *n, *tmp; int shrunk = 0; + int loop = 0; NEIGH_CACHE_STAT_INC(tbl, forced_gc_runs); @@ -279,10 +281,16 @@ static int neigh_forced_gc(struct neigh_table *tbl) if (shrunk >= max_clean) break; } + if (++loop == 16) { + if (ktime_get_ns() > tmax) + goto unlock; + loop = 0; + } } WRITE_ONCE(tbl->last_flush, jiffies); +unlock: write_unlock_bh(&tbl->lock); return shrunk;
Powered by blists - more mailing lists