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Fri, 16 Oct 2020 10:58:43 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 0506FAF2C; Fri, 16 Oct 2020 10:58:43 +0000 (UTC) X-Outflank-Mailman: Message body and most headers restored to incoming version X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 30c2c371-37aa-4819-8685-6c2344435553 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1602845923; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=GA8cfExfO91DV4o2HCBW/wxrfYxYGPyymWSFttFyle0=; b=oyWCzUuRnsUKEe6Nm2d3xCa49BRPUirIjlYiXC5qd8xVy+2Au4YfEfAs+HqcFZL0yxGNSY cqULpZD32UO+ZLwkjAw8bRE+gqzcEVzwKCOSkfKhBY1MWig0Ma2Byurbg2V55p2U2267cG UXCMdlpOJeBMFT2d+rTbt59PV34CSOU= From: Juergen Gross To: xen-devel@lists.xenproject.org Cc: Juergen Gross , Jan Beulich , Andrew Cooper , =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= , Wei Liu , George Dunlap , Ian Jackson , Julien Grall , Stefano Stabellini Subject: [PATCH v3 2/2] xen/evtchn: rework per event channel lock Date: Fri, 16 Oct 2020 12:58:39 +0200 Message-Id: <20201016105839.14796-3-jgross@suse.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20201016105839.14796-1-jgross@suse.com> References: <20201016105839.14796-1-jgross@suse.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ZohoMail-DKIM: pass (identity @suse.com) Content-Type: text/plain; charset="utf-8" Currently the lock for a single event channel needs to be taken with interrupts off, which causes deadlocks in some cases. Rework the per event channel lock to be non-blocking for the case of sending an event and removing the need for disabling interrupts for taking the lock. The lock is needed for avoiding races between sending an event or querying the channel's state against removal of the event channel. Use a locking scheme similar to a rwlock, but with some modifications: - sending an event or querying the event channel's state uses an operation similar to read_trylock(), in case of not obtaining the lock the sending is omitted or a default state is returned - closing an event channel is similar to write_lock(), but without real fairness regarding multiple writers (this saves some space in the event channel structure and multiple writers are impossible as closing an event channel requires the domain's event_lock to be held). Fixes: e045199c7c9c54 ("evtchn: address races with evtchn_reset()") Signed-off-by: Juergen Gross --- V3: - corrected a copy-and-paste error (Jan Beulich) - corrected unlocking in two cases (Jan Beulich) - renamed evtchn_read_trylock() (Jan Beulich) - added some comments and an ASSERT() for evtchn_write_lock() - set EVENT_WRITE_LOCK_INC to INT_MIN V2: - added needed barriers Signed-off-by: Juergen Gross --- xen/arch/x86/irq.c | 6 +- xen/arch/x86/pv/shim.c | 9 +-- xen/common/event_channel.c | 109 +++++++++++++++++-------------------- xen/include/xen/event.h | 76 ++++++++++++++++++++++---- xen/include/xen/sched.h | 2 +- 5 files changed, 125 insertions(+), 77 deletions(-) diff --git a/xen/arch/x86/irq.c b/xen/arch/x86/irq.c index 93c4fb9a79..8d1f9a9fc6 100644 --- a/xen/arch/x86/irq.c +++ b/xen/arch/x86/irq.c @@ -2495,14 +2495,12 @@ static void dump_irqs(unsigned char key) pirq =3D domain_irq_to_pirq(d, irq); info =3D pirq_info(d, pirq); evtchn =3D evtchn_from_port(d, info->evtchn); - local_irq_disable(); - if ( spin_trylock(&evtchn->lock) ) + if ( evtchn_read_trylock(evtchn) ) { pending =3D evtchn_is_pending(d, evtchn); masked =3D evtchn_is_masked(d, evtchn); - spin_unlock(&evtchn->lock); + evtchn_read_unlock(evtchn); } - local_irq_enable(); printk("d%d:%3d(%c%c%c)%c", d->domain_id, pirq, "-P?"[pending], "-M?"[masked], info->masked ? 'M' : '-', diff --git a/xen/arch/x86/pv/shim.c b/xen/arch/x86/pv/shim.c index 9aef7a860a..b4e83e0778 100644 --- a/xen/arch/x86/pv/shim.c +++ b/xen/arch/x86/pv/shim.c @@ -660,11 +660,12 @@ void pv_shim_inject_evtchn(unsigned int port) if ( port_is_valid(guest, port) ) { struct evtchn *chn =3D evtchn_from_port(guest, port); - unsigned long flags; =20 - spin_lock_irqsave(&chn->lock, flags); - evtchn_port_set_pending(guest, chn->notify_vcpu_id, chn); - spin_unlock_irqrestore(&chn->lock, flags); + if ( evtchn_read_trylock(chn) ) + { + evtchn_port_set_pending(guest, chn->notify_vcpu_id, chn); + evtchn_read_unlock(chn); + } } } =20 diff --git a/xen/common/event_channel.c b/xen/common/event_channel.c index e365b5498f..3df73dbc71 100644 --- a/xen/common/event_channel.c +++ b/xen/common/event_channel.c @@ -131,7 +131,7 @@ static struct evtchn *alloc_evtchn_bucket(struct domain= *d, unsigned int port) return NULL; } chn[i].port =3D port + i; - spin_lock_init(&chn[i].lock); + atomic_set(&chn[i].lock, 0); } return chn; } @@ -253,7 +253,6 @@ static long evtchn_alloc_unbound(evtchn_alloc_unbound_t= *alloc) int port; domid_t dom =3D alloc->dom; long rc; - unsigned long flags; =20 d =3D rcu_lock_domain_by_any_id(dom); if ( d =3D=3D NULL ) @@ -269,14 +268,14 @@ static long evtchn_alloc_unbound(evtchn_alloc_unbound= _t *alloc) if ( rc ) goto out; =20 - spin_lock_irqsave(&chn->lock, flags); + evtchn_write_lock(chn); =20 chn->state =3D ECS_UNBOUND; if ( (chn->u.unbound.remote_domid =3D alloc->remote_dom) =3D=3D DOMID_= SELF ) chn->u.unbound.remote_domid =3D current->domain->domain_id; evtchn_port_init(d, chn); =20 - spin_unlock_irqrestore(&chn->lock, flags); + evtchn_write_unlock(chn); =20 alloc->port =3D port; =20 @@ -289,32 +288,26 @@ static long evtchn_alloc_unbound(evtchn_alloc_unbound= _t *alloc) } =20 =20 -static unsigned long double_evtchn_lock(struct evtchn *lchn, - struct evtchn *rchn) +static void double_evtchn_lock(struct evtchn *lchn, struct evtchn *rchn) { - unsigned long flags; - if ( lchn <=3D rchn ) { - spin_lock_irqsave(&lchn->lock, flags); + evtchn_write_lock(lchn); if ( lchn !=3D rchn ) - spin_lock(&rchn->lock); + evtchn_write_lock(rchn); } else { - spin_lock_irqsave(&rchn->lock, flags); - spin_lock(&lchn->lock); + evtchn_write_lock(rchn); + evtchn_write_lock(lchn); } - - return flags; } =20 -static void double_evtchn_unlock(struct evtchn *lchn, struct evtchn *rchn, - unsigned long flags) +static void double_evtchn_unlock(struct evtchn *lchn, struct evtchn *rchn) { if ( lchn !=3D rchn ) - spin_unlock(&lchn->lock); - spin_unlock_irqrestore(&rchn->lock, flags); + evtchn_write_unlock(lchn); + evtchn_write_unlock(rchn); } =20 static long evtchn_bind_interdomain(evtchn_bind_interdomain_t *bind) @@ -324,7 +317,6 @@ static long evtchn_bind_interdomain(evtchn_bind_interdo= main_t *bind) int lport, rport =3D bind->remote_port; domid_t rdom =3D bind->remote_dom; long rc; - unsigned long flags; =20 if ( rdom =3D=3D DOMID_SELF ) rdom =3D current->domain->domain_id; @@ -360,7 +352,7 @@ static long evtchn_bind_interdomain(evtchn_bind_interdo= main_t *bind) if ( rc ) goto out; =20 - flags =3D double_evtchn_lock(lchn, rchn); + double_evtchn_lock(lchn, rchn); =20 lchn->u.interdomain.remote_dom =3D rd; lchn->u.interdomain.remote_port =3D rport; @@ -377,7 +369,7 @@ static long evtchn_bind_interdomain(evtchn_bind_interdo= main_t *bind) */ evtchn_port_set_pending(ld, lchn->notify_vcpu_id, lchn); =20 - double_evtchn_unlock(lchn, rchn, flags); + double_evtchn_unlock(lchn, rchn); =20 bind->local_port =3D lport; =20 @@ -400,7 +392,6 @@ int evtchn_bind_virq(evtchn_bind_virq_t *bind, evtchn_p= ort_t port) struct domain *d =3D current->domain; int virq =3D bind->virq, vcpu =3D bind->vcpu; int rc =3D 0; - unsigned long flags; =20 if ( (virq < 0) || (virq >=3D ARRAY_SIZE(v->virq_to_evtchn)) ) return -EINVAL; @@ -438,14 +429,14 @@ int evtchn_bind_virq(evtchn_bind_virq_t *bind, evtchn= _port_t port) =20 chn =3D evtchn_from_port(d, port); =20 - spin_lock_irqsave(&chn->lock, flags); + evtchn_write_lock(chn); =20 chn->state =3D ECS_VIRQ; chn->notify_vcpu_id =3D vcpu; chn->u.virq =3D virq; evtchn_port_init(d, chn); =20 - spin_unlock_irqrestore(&chn->lock, flags); + evtchn_write_unlock(chn); =20 v->virq_to_evtchn[virq] =3D bind->port =3D port; =20 @@ -462,7 +453,6 @@ static long evtchn_bind_ipi(evtchn_bind_ipi_t *bind) struct domain *d =3D current->domain; int port, vcpu =3D bind->vcpu; long rc =3D 0; - unsigned long flags; =20 if ( domain_vcpu(d, vcpu) =3D=3D NULL ) return -ENOENT; @@ -474,13 +464,13 @@ static long evtchn_bind_ipi(evtchn_bind_ipi_t *bind) =20 chn =3D evtchn_from_port(d, port); =20 - spin_lock_irqsave(&chn->lock, flags); + evtchn_write_lock(chn); =20 chn->state =3D ECS_IPI; chn->notify_vcpu_id =3D vcpu; evtchn_port_init(d, chn); =20 - spin_unlock_irqrestore(&chn->lock, flags); + evtchn_write_unlock(chn); =20 bind->port =3D port; =20 @@ -524,7 +514,6 @@ static long evtchn_bind_pirq(evtchn_bind_pirq_t *bind) struct pirq *info; int port =3D 0, pirq =3D bind->pirq; long rc; - unsigned long flags; =20 if ( (pirq < 0) || (pirq >=3D d->nr_pirqs) ) return -EINVAL; @@ -557,14 +546,14 @@ static long evtchn_bind_pirq(evtchn_bind_pirq_t *bind) goto out; } =20 - spin_lock_irqsave(&chn->lock, flags); + evtchn_write_lock(chn); =20 chn->state =3D ECS_PIRQ; chn->u.pirq.irq =3D pirq; link_pirq_port(port, chn, v); evtchn_port_init(d, chn); =20 - spin_unlock_irqrestore(&chn->lock, flags); + evtchn_write_unlock(chn); =20 bind->port =3D port; =20 @@ -585,7 +574,6 @@ int evtchn_close(struct domain *d1, int port1, bool gue= st) struct evtchn *chn1, *chn2; int port2; long rc =3D 0; - unsigned long flags; =20 again: spin_lock(&d1->event_lock); @@ -686,14 +674,14 @@ int evtchn_close(struct domain *d1, int port1, bool g= uest) BUG_ON(chn2->state !=3D ECS_INTERDOMAIN); BUG_ON(chn2->u.interdomain.remote_dom !=3D d1); =20 - flags =3D double_evtchn_lock(chn1, chn2); + double_evtchn_lock(chn1, chn2); =20 evtchn_free(d1, chn1); =20 chn2->state =3D ECS_UNBOUND; chn2->u.unbound.remote_domid =3D d1->domain_id; =20 - double_evtchn_unlock(chn1, chn2, flags); + double_evtchn_unlock(chn1, chn2); =20 goto out; =20 @@ -701,9 +689,9 @@ int evtchn_close(struct domain *d1, int port1, bool gue= st) BUG(); } =20 - spin_lock_irqsave(&chn1->lock, flags); + evtchn_write_lock(chn1); evtchn_free(d1, chn1); - spin_unlock_irqrestore(&chn1->lock, flags); + evtchn_write_unlock(chn1); =20 out: if ( d2 !=3D NULL ) @@ -723,7 +711,6 @@ int evtchn_send(struct domain *ld, unsigned int lport) struct evtchn *lchn, *rchn; struct domain *rd; int rport, ret =3D 0; - unsigned long flags; =20 if ( !port_is_valid(ld, lport) ) return -EINVAL; @@ -736,7 +723,8 @@ int evtchn_send(struct domain *ld, unsigned int lport) =20 lchn =3D evtchn_from_port(ld, lport); =20 - spin_lock_irqsave(&lchn->lock, flags); + if ( !evtchn_read_trylock(lchn) ) + return 0; =20 /* Guest cannot send via a Xen-attached event channel. */ if ( unlikely(consumer_is_xen(lchn)) ) @@ -771,7 +759,7 @@ int evtchn_send(struct domain *ld, unsigned int lport) } =20 out: - spin_unlock_irqrestore(&lchn->lock, flags); + evtchn_read_unlock(lchn); =20 return ret; } @@ -798,9 +786,11 @@ void send_guest_vcpu_virq(struct vcpu *v, uint32_t vir= q) =20 d =3D v->domain; chn =3D evtchn_from_port(d, port); - spin_lock(&chn->lock); - evtchn_port_set_pending(d, v->vcpu_id, chn); - spin_unlock(&chn->lock); + if ( evtchn_read_trylock(chn) ) + { + evtchn_port_set_pending(d, v->vcpu_id, chn); + evtchn_read_unlock(chn); + } =20 out: spin_unlock_irqrestore(&v->virq_lock, flags); @@ -829,9 +819,11 @@ void send_guest_global_virq(struct domain *d, uint32_t= virq) goto out; =20 chn =3D evtchn_from_port(d, port); - spin_lock(&chn->lock); - evtchn_port_set_pending(d, chn->notify_vcpu_id, chn); - spin_unlock(&chn->lock); + if ( evtchn_read_trylock(chn) ) + { + evtchn_port_set_pending(d, chn->notify_vcpu_id, chn); + evtchn_read_unlock(chn); + } =20 out: spin_unlock_irqrestore(&v->virq_lock, flags); @@ -841,7 +833,6 @@ void send_guest_pirq(struct domain *d, const struct pir= q *pirq) { int port; struct evtchn *chn; - unsigned long flags; =20 /* * PV guests: It should not be possible to race with __evtchn_close().= The @@ -856,9 +847,11 @@ void send_guest_pirq(struct domain *d, const struct pi= rq *pirq) } =20 chn =3D evtchn_from_port(d, port); - spin_lock_irqsave(&chn->lock, flags); - evtchn_port_set_pending(d, chn->notify_vcpu_id, chn); - spin_unlock_irqrestore(&chn->lock, flags); + if ( evtchn_read_trylock(chn) ) + { + evtchn_port_set_pending(d, chn->notify_vcpu_id, chn); + evtchn_read_unlock(chn); + } } =20 static struct domain *global_virq_handlers[NR_VIRQS] __read_mostly; @@ -1060,15 +1053,16 @@ int evtchn_unmask(unsigned int port) { struct domain *d =3D current->domain; struct evtchn *evtchn; - unsigned long flags; =20 if ( unlikely(!port_is_valid(d, port)) ) return -EINVAL; =20 evtchn =3D evtchn_from_port(d, port); - spin_lock_irqsave(&evtchn->lock, flags); - evtchn_port_unmask(d, evtchn); - spin_unlock_irqrestore(&evtchn->lock, flags); + if ( evtchn_read_trylock(evtchn) ) + { + evtchn_port_unmask(d, evtchn); + evtchn_read_unlock(evtchn); + } =20 return 0; } @@ -1327,7 +1321,6 @@ int alloc_unbound_xen_event_channel( { struct evtchn *chn; int port, rc; - unsigned long flags; =20 spin_lock(&ld->event_lock); =20 @@ -1340,14 +1333,14 @@ int alloc_unbound_xen_event_channel( if ( rc ) goto out; =20 - spin_lock_irqsave(&chn->lock, flags); + evtchn_write_lock(chn); =20 chn->state =3D ECS_UNBOUND; chn->xen_consumer =3D get_xen_consumer(notification_fn); chn->notify_vcpu_id =3D lvcpu; chn->u.unbound.remote_domid =3D remote_domid; =20 - spin_unlock_irqrestore(&chn->lock, flags); + evtchn_write_unlock(chn); =20 /* * Increment ->xen_evtchns /after/ ->active_evtchns. No explicit @@ -1383,7 +1376,6 @@ void notify_via_xen_event_channel(struct domain *ld, = int lport) { struct evtchn *lchn, *rchn; struct domain *rd; - unsigned long flags; =20 if ( !port_is_valid(ld, lport) ) { @@ -1398,7 +1390,8 @@ void notify_via_xen_event_channel(struct domain *ld, = int lport) =20 lchn =3D evtchn_from_port(ld, lport); =20 - spin_lock_irqsave(&lchn->lock, flags); + if ( !evtchn_read_trylock(lchn) ) + return; =20 if ( likely(lchn->state =3D=3D ECS_INTERDOMAIN) ) { @@ -1408,7 +1401,7 @@ void notify_via_xen_event_channel(struct domain *ld, = int lport) evtchn_port_set_pending(rd, rchn->notify_vcpu_id, rchn); } =20 - spin_unlock_irqrestore(&lchn->lock, flags); + evtchn_read_unlock(lchn); } =20 void evtchn_check_pollers(struct domain *d, unsigned int port) diff --git a/xen/include/xen/event.h b/xen/include/xen/event.h index 509d3ae861..592e0dc22d 100644 --- a/xen/include/xen/event.h +++ b/xen/include/xen/event.h @@ -105,6 +105,60 @@ void notify_via_xen_event_channel(struct domain *ld, i= nt lport); #define bucket_from_port(d, p) \ ((group_from_port(d, p))[((p) % EVTCHNS_PER_GROUP) / EVTCHNS_PER_BUCKE= T]) =20 +#define EVENT_WRITE_LOCK_INC INT_MIN + +/* + * Lock an event channel exclusively. This is allowed only with holding + * d->event_lock AND when the channel is free or unbound either when taking + * or when releasing the lock, as any concurrent operation on the event + * channel using evtchn_read_trylock() will just assume the event channel = is + * free or unbound at the moment. + */ +static inline void evtchn_write_lock(struct evtchn *evtchn) +{ + int val; + + /* + * The lock can't be held by a writer already, as all writers need to + * hold d->event_lock. + */ + ASSERT(atomic_read(&evtchn->lock) >=3D 0); + + /* No barrier needed, atomic_add_return() is full barrier. */ + for ( val =3D atomic_add_return(EVENT_WRITE_LOCK_INC, &evtchn->lock); + val !=3D EVENT_WRITE_LOCK_INC; + val =3D atomic_read(&evtchn->lock) ) + cpu_relax(); +} + +static inline void evtchn_write_unlock(struct evtchn *evtchn) +{ + arch_lock_release_barrier(); + + atomic_sub(EVENT_WRITE_LOCK_INC, &evtchn->lock); +} + +static inline bool evtchn_read_trylock(struct evtchn *evtchn) +{ + if ( atomic_read(&evtchn->lock) < 0 ) + return false; + + /* No barrier needed, atomic_inc_return() is full barrier. */ + if ( atomic_inc_return(&evtchn->lock) >=3D 0 ) + return true; + + atomic_dec(&evtchn->lock); + + return false; +} + +static inline void evtchn_read_unlock(struct evtchn *evtchn) +{ + arch_lock_release_barrier(); + + atomic_dec(&evtchn->lock); +} + static inline unsigned int max_evtchns(const struct domain *d) { return d->evtchn_fifo ? EVTCHN_FIFO_NR_CHANNELS @@ -249,12 +303,13 @@ static inline bool evtchn_is_masked(const struct doma= in *d, static inline bool evtchn_port_is_masked(struct domain *d, evtchn_port_t p= ort) { struct evtchn *evtchn =3D evtchn_from_port(d, port); - bool rc; - unsigned long flags; + bool rc =3D true; =20 - spin_lock_irqsave(&evtchn->lock, flags); - rc =3D evtchn_is_masked(d, evtchn); - spin_unlock_irqrestore(&evtchn->lock, flags); + if ( evtchn_read_trylock(evtchn) ) + { + rc =3D evtchn_is_masked(d, evtchn); + evtchn_read_unlock(evtchn); + } =20 return rc; } @@ -274,12 +329,13 @@ static inline int evtchn_port_poll(struct domain *d, = evtchn_port_t port) if ( port_is_valid(d, port) ) { struct evtchn *evtchn =3D evtchn_from_port(d, port); - unsigned long flags; =20 - spin_lock_irqsave(&evtchn->lock, flags); - if ( evtchn_usable(evtchn) ) - rc =3D evtchn_is_pending(d, evtchn); - spin_unlock_irqrestore(&evtchn->lock, flags); + if ( evtchn_read_trylock(evtchn) ) + { + if ( evtchn_usable(evtchn) ) + rc =3D evtchn_is_pending(d, evtchn); + evtchn_read_unlock(evtchn); + } } =20 return rc; diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h index a298ff4df8..096e0ec6af 100644 --- a/xen/include/xen/sched.h +++ b/xen/include/xen/sched.h @@ -85,7 +85,7 @@ extern domid_t hardware_domid; =20 struct evtchn { - spinlock_t lock; + atomic_t lock; /* kind of rwlock, use evtchn_*_[un]lock() = */ #define ECS_FREE 0 /* Channel is available for use. = */ #define ECS_RESERVED 1 /* Channel is reserved. = */ #define ECS_UNBOUND 2 /* Channel is waiting to bind to a remote domai= n. */ --=20 2.26.2