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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , mleitner@redhat.com, David Ahern , Juri Lelli , Tomas Glozar , Sebastian Andrzej Siewior , Thomas Gleixner Subject: [PATCH v5 2/2] tcp/dcpp: Un-pin tw_timer Date: Mon, 15 Apr 2024 13:34:36 +0200 Message-ID: <20240415113436.3261042-3-vschneid@redhat.com> In-Reply-To: <20240415113436.3261042-1-vschneid@redhat.com> References: <20240415113436.3261042-1-vschneid@redhat.com> Precedence: bulk X-Mailing-List: linux-rt-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.7 Context ======= 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 e02b93124855 ("workqueue: Unbind kworkers before sending them to exit()") Changes ======= 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() Lastly, to prevent the ehash lock from being taken both in timer context and in timer deletion context (which leads to deadlocks), move the inet_twsk_kill() from timer expiry context to workqueue context by changing the tw_timer to a delayed_work. Thanks to Paolo for suggesting to leverage the ehash lock. Note on partial reverts ======================= This partially reverts ec94c2696f0b ("tcp/dccp: avoid one atomic operation for timewait hashdance") This also reinstores a comment from 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. Link: https://lore.kernel.org/all/ZPhpfMjSiHVjQkTk@localhost.localdomain/ Signed-off-by: Valentin Schneider --- include/net/inet_timewait_sock.h | 6 ++-- net/dccp/minisocks.c | 9 +++-- net/ipv4/inet_timewait_sock.c | 59 +++++++++++++++++++++++--------- net/ipv4/tcp_minisocks.c | 9 +++-- 4 files changed, 55 insertions(+), 28 deletions(-) diff --git a/include/net/inet_timewait_sock.h b/include/net/inet_timewait_sock.h index c4d64f1f8d415..93a50eed41872 100644 --- a/include/net/inet_timewait_sock.h +++ b/include/net/inet_timewait_sock.h @@ -93,8 +93,10 @@ struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk, 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); diff --git a/net/dccp/minisocks.c b/net/dccp/minisocks.c index 64d805b27adde..dd0b09553f142 100644 --- a/net/dccp/minisocks.c +++ b/net/dccp/minisocks.c @@ -58,11 +58,10 @@ void dccp_time_wait(struct sock *sk, int state, int timeo) * 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); + /* Linkage updates. */ + inet_twsk_hashdance_schedule(tw, sk, &dccp_hashinfo, timeo); + /* Access to tw after this point is illegal. */ + inet_twsk_put(tw); local_bh_enable(); } else { /* Sorry, if we're out of memory, just CLOSE this diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c index 7a2dcbaa1a61e..165b9cdf27e1a 100644 --- a/net/ipv4/inet_timewait_sock.c +++ b/net/ipv4/inet_timewait_sock.c @@ -44,14 +44,14 @@ void inet_twsk_bind_unhash(struct inet_timewait_sock *tw, __sock_put((struct sock *)tw); } -/* Must be called with locally disabled BHs. */ -static void inet_twsk_kill(struct inet_timewait_sock *tw) +static void __inet_twsk_kill(struct inet_timewait_sock *tw, spinlock_t *lock) +__releases(lock) { struct inet_hashinfo *hashinfo = tw->tw_dr->hashinfo; - spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash); struct inet_bind_hashbucket *bhead, *bhead2; - spin_lock(lock); + lockdep_assert_held(lock); + sk_nulls_del_node_init_rcu((struct sock *)tw); spin_unlock(lock); @@ -71,6 +71,16 @@ static void inet_twsk_kill(struct inet_timewait_sock *tw) inet_twsk_put(tw); } +/* Must be called with locally disabled BHs. */ +static void inet_twsk_kill(struct inet_timewait_sock *tw) +{ + struct inet_hashinfo *hashinfo = tw->tw_dr->hashinfo; + spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash); + + spin_lock(lock); + __inet_twsk_kill(tw, lock); +} + void inet_twsk_free(struct inet_timewait_sock *tw) { struct module *owner = tw->tw_prot->owner; @@ -97,8 +107,10 @@ static void inet_twsk_add_node_rcu(struct inet_timewait_sock *tw, * Essentially we whip up a timewait bucket, copy the relevant info into it * from the SK, and mess with hash chains and list linkage. */ -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 +141,33 @@ void inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk, 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); - /* tw_refcnt is set to 3 because we have : + /* Ensure above writes are committed into memory before updating the + * refcount. + * Provides ordering vs later refcount_inc(). + */ + smp_wmb(); + /* tw_refcnt is set to 4 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. + * - one reference for ourself (our caller will release it). */ - refcount_set(&tw->tw_refcnt, 3); + refcount_set(&tw->tw_refcnt, 4); + + inet_twsk_schedule(tw, timeo); + + spin_unlock(lock); + } -EXPORT_SYMBOL_GPL(inet_twsk_hashdance); +EXPORT_SYMBOL_GPL(inet_twsk_hashdance_schedule); static void tw_expiry_workfn(struct work_struct *work) { @@ -219,8 +238,16 @@ EXPORT_SYMBOL_GPL(inet_twsk_alloc); */ void inet_twsk_deschedule_put(struct inet_timewait_sock *tw) { - if (cancel_delayed_work_sync(&tw->tw_expiry_work)) - inet_twsk_kill(tw); + struct inet_hashinfo *hashinfo = tw->tw_dr->hashinfo; + spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash); + + spin_lock(lock); + if (cancel_delayed_work_sync(&tw->tw_expiry_work)) { + /* releases @lock */ + __inet_twsk_kill(tw, lock); + } else { + spin_unlock(lock); + } inet_twsk_put(tw); } EXPORT_SYMBOL(inet_twsk_deschedule_put); diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c index f0761f060a837..77e2515409e40 100644 --- a/net/ipv4/tcp_minisocks.c +++ b/net/ipv4/tcp_minisocks.c @@ -343,11 +343,10 @@ void tcp_time_wait(struct sock *sk, int state, int timeo) * 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); + /* Linkage updates. */ + inet_twsk_hashdance_schedule(tw, sk, net->ipv4.tcp_death_row.hashinfo, timeo); + /* Access to tw after this point is illegal. */ + inet_twsk_put(tw); local_bh_enable(); } else { /* Sorry, if we're out of memory, just CLOSE this