diff options
Diffstat (limited to 'debian/patches-rt/0001-net-tcp-dccp-prepare-for-tw_timer-un-pinning.patch')
| -rw-r--r-- | debian/patches-rt/0001-net-tcp-dccp-prepare-for-tw_timer-un-pinning.patch | 188 |
1 files changed, 188 insertions, 0 deletions
diff --git a/debian/patches-rt/0001-net-tcp-dccp-prepare-for-tw_timer-un-pinning.patch b/debian/patches-rt/0001-net-tcp-dccp-prepare-for-tw_timer-un-pinning.patch new file mode 100644 index 0000000000..7fd7164b95 --- /dev/null +++ b/debian/patches-rt/0001-net-tcp-dccp-prepare-for-tw_timer-un-pinning.patch @@ -0,0 +1,188 @@ +From: Valentin Schneider <vschneid@redhat.com> +Date: Tue, 4 Jun 2024 16:08:47 +0200 +Subject: [PATCH 1/3] net: tcp/dccp: prepare for tw_timer un-pinning +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.10/older/patches-6.10.2-rt14.tar.xz + +The TCP timewait timer is proving to be problematic for setups where +scheduler CPU isolation is achieved at runtime via cpusets (as opposed to +statically via isolcpus=domains). + +What happens there is a CPU goes through tcp_time_wait(), arming the +time_wait timer, then gets isolated. TCP_TIMEWAIT_LEN later, the timer +fires, causing interference for the now-isolated CPU. This is conceptually +similar to the issue described in commit e02b93124855 ("workqueue: Unbind +kworkers before sending them to exit()") + +Move inet_twsk_schedule() to within inet_twsk_hashdance(), with the ehash +lock held. Expand the lock's critical section from inet_twsk_kill() to +inet_twsk_deschedule_put(), serializing the scheduling vs descheduling of +the timer. IOW, this prevents the following race: + + tcp_time_wait() + inet_twsk_hashdance() + inet_twsk_deschedule_put() + del_timer_sync() + inet_twsk_schedule() + +Thanks to Paolo Abeni for suggesting to leverage the ehash lock. + +This also restores a comment from commit ec94c2696f0b ("tcp/dccp: avoid +one atomic operation for timewait hashdance") as inet_twsk_hashdance() had +a "Step 1" and "Step 3" comment, but the "Step 2" had gone missing. + +inet_twsk_deschedule_put() now acquires the ehash spinlock to synchronize +with inet_twsk_hashdance_schedule(). + +To ease possible regression search, actual un-pin is done in next patch. + +Link: https://lore.kernel.org/all/ZPhpfMjSiHVjQkTk@localhost.localdomain/ +Signed-off-by: Valentin Schneider <vschneid@redhat.com> +Signed-off-by: Florian Westphal <fw@strlen.de> +Reviewed-by: Eric Dumazet <edumazet@google.com> +Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +Link: https://lore.kernel.org/r/20240604140903.31939-2-fw@strlen.de +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + include/net/inet_timewait_sock.h | 6 +++- + net/dccp/minisocks.c | 3 -- + net/ipv4/inet_timewait_sock.c | 52 +++++++++++++++++++++++++++++++++------ + net/ipv4/tcp_minisocks.c | 3 -- + 4 files changed, 51 insertions(+), 13 deletions(-) + +--- a/include/net/inet_timewait_sock.h ++++ b/include/net/inet_timewait_sock.h +@@ -93,8 +93,10 @@ struct inet_timewait_sock *inet_twsk_all + struct inet_timewait_death_row *dr, + const int state); + +-void inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk, +- struct inet_hashinfo *hashinfo); ++void inet_twsk_hashdance_schedule(struct inet_timewait_sock *tw, ++ struct sock *sk, ++ struct inet_hashinfo *hashinfo, ++ int timeo); + + void __inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo, + bool rearm); +--- a/net/dccp/minisocks.c ++++ b/net/dccp/minisocks.c +@@ -59,11 +59,10 @@ void dccp_time_wait(struct sock *sk, int + * we complete the initialization. + */ + local_bh_disable(); +- inet_twsk_schedule(tw, timeo); + /* Linkage updates. + * Note that access to tw after this point is illegal. + */ +- inet_twsk_hashdance(tw, sk, &dccp_hashinfo); ++ inet_twsk_hashdance_schedule(tw, sk, &dccp_hashinfo, timeo); + local_bh_enable(); + } else { + /* Sorry, if we're out of memory, just CLOSE this +--- a/net/ipv4/inet_timewait_sock.c ++++ b/net/ipv4/inet_timewait_sock.c +@@ -96,9 +96,13 @@ static void inet_twsk_add_node_rcu(struc + * Enter the time wait state. This is called with locally disabled BH. + * Essentially we whip up a timewait bucket, copy the relevant info into it + * from the SK, and mess with hash chains and list linkage. ++ * ++ * The caller must not access @tw anymore after this function returns. + */ +-void inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk, +- struct inet_hashinfo *hashinfo) ++void inet_twsk_hashdance_schedule(struct inet_timewait_sock *tw, ++ struct sock *sk, ++ struct inet_hashinfo *hashinfo, ++ int timeo) + { + const struct inet_sock *inet = inet_sk(sk); + const struct inet_connection_sock *icsk = inet_csk(sk); +@@ -129,26 +133,33 @@ void inet_twsk_hashdance(struct inet_tim + + spin_lock(lock); + ++ /* Step 2: Hash TW into tcp ehash chain */ + inet_twsk_add_node_rcu(tw, &ehead->chain); + + /* Step 3: Remove SK from hash chain */ + if (__sk_nulls_del_node_init_rcu(sk)) + sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1); + +- spin_unlock(lock); + ++ /* Ensure above writes are committed into memory before updating the ++ * refcount. ++ * Provides ordering vs later refcount_inc(). ++ */ ++ smp_wmb(); + /* tw_refcnt is set to 3 because we have : + * - one reference for bhash chain. + * - one reference for ehash chain. + * - one reference for timer. +- * We can use atomic_set() because prior spin_lock()/spin_unlock() +- * committed into memory all tw fields. + * Also note that after this point, we lost our implicit reference + * so we are not allowed to use tw anymore. + */ + refcount_set(&tw->tw_refcnt, 3); ++ ++ inet_twsk_schedule(tw, timeo); ++ ++ spin_unlock(lock); + } +-EXPORT_SYMBOL_GPL(inet_twsk_hashdance); ++EXPORT_SYMBOL_GPL(inet_twsk_hashdance_schedule); + + static void tw_timer_handler(struct timer_list *t) + { +@@ -217,7 +228,34 @@ EXPORT_SYMBOL_GPL(inet_twsk_alloc); + */ + void inet_twsk_deschedule_put(struct inet_timewait_sock *tw) + { +- if (del_timer_sync(&tw->tw_timer)) ++ struct inet_hashinfo *hashinfo = tw->tw_dr->hashinfo; ++ spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash); ++ ++ /* inet_twsk_purge() walks over all sockets, including tw ones, ++ * and removes them via inet_twsk_deschedule_put() after a ++ * refcount_inc_not_zero(). ++ * ++ * inet_twsk_hashdance_schedule() must (re)init the refcount before ++ * arming the timer, i.e. inet_twsk_purge can obtain a reference to ++ * a twsk that did not yet schedule the timer. ++ * ++ * The ehash lock synchronizes these two: ++ * After acquiring the lock, the timer is always scheduled (else ++ * timer_shutdown returns false), because hashdance_schedule releases ++ * the ehash lock only after completing the timer initialization. ++ * ++ * Without grabbing the ehash lock, we get: ++ * 1) cpu x sets twsk refcount to 3 ++ * 2) cpu y bumps refcount to 4 ++ * 3) cpu y calls inet_twsk_deschedule_put() and shuts timer down ++ * 4) cpu x tries to start timer, but mod_timer is a noop post-shutdown ++ * -> timer refcount is never decremented. ++ */ ++ spin_lock(lock); ++ /* Makes sure hashdance_schedule() has completed */ ++ spin_unlock(lock); ++ ++ if (timer_shutdown_sync(&tw->tw_timer)) + inet_twsk_kill(tw); + inet_twsk_put(tw); + } +--- a/net/ipv4/tcp_minisocks.c ++++ b/net/ipv4/tcp_minisocks.c +@@ -344,11 +344,10 @@ void tcp_time_wait(struct sock *sk, int + * we complete the initialization. + */ + local_bh_disable(); +- inet_twsk_schedule(tw, timeo); + /* Linkage updates. + * Note that access to tw after this point is illegal. + */ +- inet_twsk_hashdance(tw, sk, net->ipv4.tcp_death_row.hashinfo); ++ inet_twsk_hashdance_schedule(tw, sk, net->ipv4.tcp_death_row.hashinfo, timeo); + local_bh_enable(); + } else { + /* Sorry, if we're out of memory, just CLOSE this |