Re: [dpdk-dev] [PATCH V19 2/4] eal: add failure handler mechanism for hot plug

["Zhang, Qi Z" <qi.z.zhang@intel.com>]

One more comment

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Zhang, Qi Z
> Sent: Friday, April 6, 2018 10:04 PM
> To: Guo, Jia <jia.guo@intel.com>; stephen@networkplumber.org; Richardson,
> Bruce <bruce.richardson@intel.com>; Yigit, Ferruh <ferruh.yigit@intel.com>;
> Ananyev, Konstantin <konstantin.ananyev@intel.com>;
> gaetan.rivet@6wind.com; Wu, Jingjing <jingjing.wu@intel.com>;
> thomas@monjalon.net; motih@mellanox.com; Van Haaren, Harry
> <harry.van.haaren@intel.com>; Tan, Jianfeng <jianfeng.tan@intel.com>
> Cc: jblunck@infradead.org; shreyansh.jain@nxp.com; dev@dpdk.org; Guo, Jia
> <jia.guo@intel.com>; Zhang, Helin <helin.zhang@intel.com>
> Subject: Re: [dpdk-dev] [PATCH V19 2/4] eal: add failure handler mechanism
> for hot plug
> 
> Hi Jeff:
> 
> > -----Original Message-----
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Jeff Guo
> > Sent: Friday, April 6, 2018 6:57 PM
> > To: stephen@networkplumber.org; Richardson, Bruce
> > <bruce.richardson@intel.com>; Yigit, Ferruh <ferruh.yigit@intel.com>;
> > Ananyev, Konstantin <konstantin.ananyev@intel.com>;
> > gaetan.rivet@6wind.com; Wu, Jingjing <jingjing.wu@intel.com>;
> > thomas@monjalon.net; motih@mellanox.com; Van Haaren, Harry
> > <harry.van.haaren@intel.com>; Tan, Jianfeng <jianfeng.tan@intel.com>
> > Cc: jblunck@infradead.org; shreyansh.jain@nxp.com; dev@dpdk.org; Guo,
> > Jia <jia.guo@intel.com>; Zhang, Helin <helin.zhang@intel.com>
> > Subject: [dpdk-dev] [PATCH V19 2/4] eal: add failure handler mechanism
> > for hot plug
> >
> > This patch introduces an API (rte_dev_handle_hot_unplug) to handle
> > device hot unplug event. When device be hot plug out, the device
> > resource become invalid, if this resource is still be unexpected
> > read/write, system will crash. The api let user register the hot
> > unplug handler, 

The description is a little bit misleading , based on current implementation.
it does not a function that let user "register a handler", actually It let user to
"set a recover point" when some exception (like sigbus) happen due to hot unplug.
Maybe the function name could be changed also, 
for example: rte_dev_set_recover_point.

> when hot plug failure occur, the working thread will
> > be block until the uevent mechanism successful recovery the memory and
> guaranty the application keep running smoothly.
> >
> > Signed-off-by: Jeff Guo <jia.guo@intel.com>
> > ---
> > v19->18:
> > add note for limitation of multiple hotplug
> > ---
> >  doc/guides/rel_notes/release_18_05.rst  |   6 ++
> >  kernel/linux/igb_uio/igb_uio.c          |   4 +
> >  lib/librte_eal/common/include/rte_dev.h |  19 +++++
> >  lib/librte_eal/linuxapp/eal/eal_dev.c   | 140
> > +++++++++++++++++++++++++++++++-
> >  lib/librte_eal/rte_eal_version.map      |   1 +
> >  5 files changed, 169 insertions(+), 1 deletion(-)
> >
> > diff --git a/doc/guides/rel_notes/release_18_05.rst
> > b/doc/guides/rel_notes/release_18_05.rst
> > index cb9e050..2707e73 100644
> > --- a/doc/guides/rel_notes/release_18_05.rst
> > +++ b/doc/guides/rel_notes/release_18_05.rst
> > @@ -70,6 +70,12 @@ New Features
> >
> >    Linux uevent is supported as backend of this device event
> > notification framework.
> >
> > +* **Added hot plug failure handler.**
> > +
> > +  Added a failure handler machenism to handle hot unplug device.
> > +
> > +  * ``rte_dev_handle_hot_unplug`` for handle hot unplug device failure.
> > +
> >  API Changes
> >  -----------
> >
> > diff --git a/kernel/linux/igb_uio/igb_uio.c
> > b/kernel/linux/igb_uio/igb_uio.c index 4cae4dd..293c310 100644
> > --- a/kernel/linux/igb_uio/igb_uio.c
> > +++ b/kernel/linux/igb_uio/igb_uio.c
> > @@ -344,6 +344,10 @@ igbuio_pci_release(struct uio_info *info, struct
> > inode
> > *inode)
> >  	struct rte_uio_pci_dev *udev = info->priv;
> >  	struct pci_dev *dev = udev->pdev;
> >
> > +	/* check if device has been remove before release */
> > +	if ((&dev->dev.kobj)->state_remove_uevent_sent == 1)
> > +		return -1;
> > +
> >  	mutex_lock(&udev->lock);
> >  	if (--udev->refcnt > 0) {
> >  		mutex_unlock(&udev->lock);
> > diff --git a/lib/librte_eal/common/include/rte_dev.h
> > b/lib/librte_eal/common/include/rte_dev.h
> > index a5203e7..17c446d 100644
> > --- a/lib/librte_eal/common/include/rte_dev.h
> > +++ b/lib/librte_eal/common/include/rte_dev.h
> > @@ -361,4 +361,23 @@ rte_dev_event_monitor_start(void);
> >   */
> >  int __rte_experimental
> >  rte_dev_event_monitor_stop(void);
> > +
> > +/**
> > + * @warning
> > + * @b EXPERIMENTAL: this API may change without prior notice
> > + *
> > + * It can be used to register the device signal bus handler, and save
> > +the
> > + * current environment for each thread, when signal bus error invoke,
> > +the
> > + * handler would restore the environment by long jmp to each working
> > + * thread previous locate, then block the thread to waiting until the
> > +memory
> > + * recovery and remapping be finished, that would guaranty the system
> > +not
> > + * crash when the device be hot unplug.
> > + *
> > + * @param none
> > + * @return
> > + *   - From a successful direct invocation, zero.
> > + *   - From a call of siglongjmp(), non_zero.
> > + */
> > +int __rte_experimental
> > +rte_dev_handle_hot_unplug(void);
> >  #endif /* _RTE_DEV_H_ */
> > diff --git a/lib/librte_eal/linuxapp/eal/eal_dev.c
> > b/lib/librte_eal/linuxapp/eal/eal_dev.c
> > index 9478a39..84b7efc 100644
> > --- a/lib/librte_eal/linuxapp/eal/eal_dev.c
> > +++ b/lib/librte_eal/linuxapp/eal/eal_dev.c
> > @@ -4,6 +4,9 @@
> >
> >  #include <string.h>
> >  #include <unistd.h>
> > +#include <signal.h>
> > +#include <setjmp.h>
> > +#include <pthread.h>
> >  #include <sys/socket.h>
> >  #include <linux/netlink.h>
> >
> > @@ -13,12 +16,17 @@
> >  #include <rte_malloc.h>
> >  #include <rte_interrupts.h>
> >  #include <rte_alarm.h>
> > +#include <rte_bus.h>
> > +#include <rte_per_lcore.h>
> >
> >  #include "eal_private.h"
> >
> >  static struct rte_intr_handle intr_handle = {.fd = -1 };  static bool
> > monitor_started;
> >
> > +pthread_mutex_t failure_recovery_lock; pthread_cond_t
> > +failure_recovery_cond;
> > +
> >  #define EAL_UEV_MSG_LEN 4096
> >  #define EAL_UEV_MSG_ELEM_LEN 128
> >
> > @@ -32,6 +40,22 @@ enum eal_dev_event_subsystem {
> >  	EAL_DEV_EVENT_SUBSYSTEM_MAX
> >  };
> >
> > +static RTE_DEFINE_PER_LCORE(sigjmp_buf, unplug_longjmp_env);
> > +
> > +static void sigbus_handler(int signum __rte_unused) {
> > +	RTE_LOG(DEBUG, EAL, "receive SIGBUS error!\n");
> > +	siglongjmp(RTE_PER_LCORE(unplug_longjmp_env), 1); }
> > +
> > +static int cmp_dev_name(const struct rte_device *dev,
> > +	const void *_name)
> > +{
> > +	const char *name = _name;
> > +
> > +	return strcmp(dev->name, name);
> > +}
> > +
> >  static int
> >  dev_uev_socket_fd_create(void)
> >  {
> > @@ -132,6 +156,31 @@ dev_uev_parse(const char *buf, struct
> > rte_dev_event *event, int length)
> >  	return 0;
> >  }
> >
> > +static int
> > +dev_uev_remove_handler(struct rte_device *dev) {
> > +	struct rte_bus *bus = rte_bus_find_by_device_name(dev->name);
> > +	int ret;
> > +
> > +	if (!dev)
> > +		return -1;
> > +
> > +	if (bus->handle_hot_unplug) {
> > +		/**
> > +		 * call bus ops to handle hot unplug.
> > +		 */
> > +		ret = bus->handle_hot_unplug(dev);
> > +		if (ret) {
> > +			RTE_LOG(ERR, EAL,
> > +				"It cannot handle hot unplug for device (%s) "
> > +				"on the bus.\n ",
> > +				dev->name);
> > +			return ret;
> > +		}
> > +	}
> > +	return 0;
> > +}
> > +
> >  static void
> >  dev_delayed_unregister(void *param)
> >  {
> > @@ -146,6 +195,9 @@ dev_uev_handler(__rte_unused void *param)
> >  	struct rte_dev_event uevent;
> >  	int ret;
> >  	char buf[EAL_UEV_MSG_LEN];
> > +	struct rte_bus *bus;
> > +	struct rte_device *dev;
> > +	const char *busname;
> >
> >  	memset(&uevent, 0, sizeof(struct rte_dev_event));
> >  	memset(buf, 0, EAL_UEV_MSG_LEN);
> > @@ -170,11 +222,87 @@ dev_uev_handler(__rte_unused void *param)
> >  	RTE_LOG(DEBUG, EAL, "receive uevent(name:%s, type:%d,
> > subsystem:%d)\n",
> >  		uevent.devname, uevent.type, uevent.subsystem);
> >
> > -	if (uevent.devname)
> > +	switch (uevent.subsystem) {
> > +	case EAL_DEV_EVENT_SUBSYSTEM_PCI:
> > +	case EAL_DEV_EVENT_SUBSYSTEM_UIO:
> > +		busname = "pci";
> > +		break;
> > +	default:
> > +		break;
> > +	}
> > +
> > +	if (uevent.devname) {
> > +		if (uevent.type == RTE_DEV_EVENT_REMOVE) {
> > +			bus = rte_bus_find_by_name(busname);
> > +			if (bus == NULL) {
> > +				RTE_LOG(ERR, EAL, "Cannot find bus (%s)\n",
> > +					uevent.devname);
> > +				return;
> > +			}
> > +			dev = bus->find_device(NULL, cmp_dev_name,
> > +					       uevent.devname);
> > +			if (dev == NULL) {
> > +				RTE_LOG(ERR, EAL,
> > +					"Cannot find unplugged device (%s)\n",
> > +					uevent.devname);
> > +				return;
> > +			}
> > +			ret = dev_uev_remove_handler(dev);
> > +			if (ret) {
> > +				RTE_LOG(ERR, EAL, "Driver cannot remap the "
> > +					"device (%s)\n",
> > +					dev->name);
> > +				return;
> > +			}
> > +			/* wake up all the threads */
> > +			pthread_cond_broadcast(&failure_recovery_cond);
> > +		}
> >  		dev_callback_process(uevent.devname, uevent.type);
> > +	}
> >  }
> >
> >  int __rte_experimental
> > +rte_dev_handle_hot_unplug(void)
> > +{
> > +	struct sigaction act;
> > +	sigset_t mask;
> > +	int ret = 0;
> > +
> > +	/* set signal handlers */
> > +	memset(&act, 0x00, sizeof(struct sigaction));
> > +	act.sa_handler = sigbus_handler;
> > +	sigemptyset(&act.sa_mask);
> > +	act.sa_flags = SA_RESTART;
> > +	sigaction(SIGBUS, &act, NULL);
> > +	sigemptyset(&mask);
> > +	sigaddset(&mask, SIGBUS);
> > +	pthread_sigmask(SIG_UNBLOCK, &mask, NULL);
> > +
> > +	ret = sigsetjmp(RTE_PER_LCORE(unplug_longjmp_env), 1);
> > +	if (ret) {
> > +		/*
> > +		 * Waitting for condition variable before failure recovery
> > +		 * finish. Now the limitation is only handle one device
> > +		 * hot plug, for multiple devices hotplug, need check if
> > +		 * the device belong to this working thread, then directly
> > +		 * call memory remaping, unrelated thread just keep going
> > +		 * their work by no interrupt from hotplug.
> > +		 * TODO: multiple device hotplug
> > +		 */
> > +		pthread_mutex_lock(&failure_recovery_lock);
> > +		RTE_LOG(DEBUG, EAL, "begin waiting for the failure handler.\n");
> > +		pthread_cond_wait(&failure_recovery_cond,
> > +					&failure_recovery_lock);
> > +		RTE_LOG(DEBUG, EAL,
> > +		       "come back from waiting for failure handler.\n");
> > +		pthread_mutex_unlock(&failure_recovery_lock);
> 
> I think we should not assume phread_cond_wait always happen before
> pthread_cond_broadcast, It is possible Sigbus just happen before remap in
> udev remove handler while pthread_cond_wait happens after
> pthread_cond_broadcast, then we will wait forever.
> 
> I think we need a flag to sync
> For example:
> 
> pthread_mutex_lock(&failure_recovery_lock);
> if ( udev_remove_handle == 0 )
> 	pthread_cond_wait(&failure_recovery_cond, & failure_recovery_lock);
> pthread_remove_handle = 0; pthread_mutex_unlock(&failure_recovery_lock);
> 
> while at remove handler:
> pthread_mutex_lock(&failure_recovery_lock);
> pthread_remove_handle = 1;
> pthread_cond_signel(&failure_recovery_cond);
> pthread_mutex_unlock(&failure_recovery_lock);
> 
> 
> Regards
> Qi
> 
> > +	}
> > +
> > +	return ret;
> > +}
> > +
> > +
> > +int __rte_experimental
> >  rte_dev_event_monitor_start(void)
> >  {
> >  	int ret;
> > @@ -196,6 +324,12 @@ rte_dev_event_monitor_start(void)
> >  		return -1;
> >  	}
> >
> > +	/* initialize mutex and condition variable
> > +	 * to control failure recovery.
> > +	 */
> > +	pthread_mutex_init(&failure_recovery_lock, NULL);
> > +	pthread_cond_init(&failure_recovery_cond, NULL);
> > +
> >  	monitor_started = true;
> >
> >  	return 0;
> > @@ -219,5 +353,9 @@ rte_dev_event_monitor_stop(void)
> >  	close(intr_handle.fd);
> >  	intr_handle.fd = -1;
> >  	monitor_started = false;
> > +
> > +	pthread_cond_destroy(&failure_recovery_cond);
> > +	pthread_mutex_destroy(&failure_recovery_lock);
> > +
> >  	return 0;
> >  }
> > diff --git a/lib/librte_eal/rte_eal_version.map
> > b/lib/librte_eal/rte_eal_version.map
> > index fc5c62a..873ef38 100644
> > --- a/lib/librte_eal/rte_eal_version.map
> > +++ b/lib/librte_eal/rte_eal_version.map
> > @@ -262,5 +262,6 @@ EXPERIMENTAL {
> >  	rte_dev_event_monitor_stop;
> >  	rte_dev_event_callback_register;
> >  	rte_dev_event_callback_unregister;
> > +	rte_dev_handle_hot_unplug;
> >
> >  } DPDK_18.02;
> > --
> > 2.7.4