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[67.48.91.116]) by smtp.gmail.com with ESMTPSA id 006d021491bc7-5e1c4e3968dsm1723644eaf.25.2024.09.10.17.14.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 10 Sep 2024 17:14:50 -0700 (PDT) Message-ID: <448875be-59e1-48a5-8a3c-cc45fff196ca@gmail.com> Date: Tue, 10 Sep 2024 19:14:46 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 3/4] driver core: shut down devices asynchronously To: Jan Kiszka , linux-kernel@vger.kernel.org, Greg Kroah-Hartman , "Rafael J . Wysocki" , Martin Belanger , Oliver O'Halloran , Daniel Wagner , Keith Busch , Lukas Wunner , David Jeffery , Jeremy Allison , Jens Axboe , Christoph Hellwig , Sagi Grimberg , linux-nvme@lists.infradead.org Cc: Nathan Chancellor References: <20240822202805.6379-1-stuart.w.hayes@gmail.com> <20240822202805.6379-4-stuart.w.hayes@gmail.com> <83f39f2d-7237-4880-83e3-1c3afc62087d@siemens.com> Content-Language: en-US From: stuart hayes In-Reply-To: <83f39f2d-7237-4880-83e3-1c3afc62087d@siemens.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/8/2024 8:36 AM, Jan Kiszka wrote: > On 22.08.24 22:28, Stuart Hayes wrote: >> Add code to allow asynchronous shutdown of devices, ensuring that each >> device is shut down before its parents & suppliers. >> >> Only devices with drivers that have async_shutdown_enable enabled will be >> shut down asynchronously. >> >> This can dramatically reduce system shutdown/reboot time on systems that >> have multiple devices that take many seconds to shut down (like certain >> NVMe drives). On one system tested, the shutdown time went from 11 minutes >> without this patch to 55 seconds with the patch. >> >> Signed-off-by: Stuart Hayes >> Signed-off-by: David Jeffery >> --- >> drivers/base/base.h | 4 +++ >> drivers/base/core.c | 54 ++++++++++++++++++++++++++++++++++- >> include/linux/device/driver.h | 2 ++ >> 3 files changed, 59 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/base/base.h b/drivers/base/base.h >> index 0b53593372d7..aa5a2bd3f2b8 100644 >> --- a/drivers/base/base.h >> +++ b/drivers/base/base.h >> @@ -10,6 +10,7 @@ >> * shared outside of the drivers/base/ directory. >> * >> */ >> +#include >> #include >> >> /** >> @@ -97,6 +98,8 @@ struct driver_private { >> * the device; typically because it depends on another driver getting >> * probed first. >> * @async_driver - pointer to device driver awaiting probe via async_probe >> + * @shutdown_after - used during device shutdown to ensure correct shutdown >> + * ordering. >> * @device - pointer back to the struct device that this structure is >> * associated with. >> * @dead - This device is currently either in the process of or has been >> @@ -114,6 +117,7 @@ struct device_private { >> struct list_head deferred_probe; >> const struct device_driver *async_driver; >> char *deferred_probe_reason; >> + async_cookie_t shutdown_after; >> struct device *device; >> u8 dead:1; >> }; >> diff --git a/drivers/base/core.c b/drivers/base/core.c >> index 7e50daa65ca0..dd3652ea56fe 100644 >> --- a/drivers/base/core.c >> +++ b/drivers/base/core.c >> @@ -9,6 +9,7 @@ >> */ >> >> #include >> +#include >> #include >> #include >> #include >> @@ -3531,6 +3532,7 @@ static int device_private_init(struct device *dev) >> klist_init(&dev->p->klist_children, klist_children_get, >> klist_children_put); >> INIT_LIST_HEAD(&dev->p->deferred_probe); >> + dev->p->shutdown_after = 0; >> return 0; >> } >> >> @@ -4781,6 +4783,8 @@ int device_change_owner(struct device *dev, kuid_t kuid, kgid_t kgid) >> } >> EXPORT_SYMBOL_GPL(device_change_owner); >> >> +static ASYNC_DOMAIN(sd_domain); >> + >> static void shutdown_one_device(struct device *dev) >> { >> /* hold lock to avoid race with probe/release */ >> @@ -4816,12 +4820,34 @@ static void shutdown_one_device(struct device *dev) >> put_device(dev->parent); >> } >> >> +/** >> + * shutdown_one_device_async >> + * @data: the pointer to the struct device to be shutdown >> + * @cookie: not used >> + * >> + * Shuts down one device, after waiting for shutdown_after to complete. >> + * shutdown_after should be set to the cookie of the last child or consumer >> + * of this device to be shutdown (if any), or to the cookie of the previous >> + * device to be shut down for devices that don't enable asynchronous shutdown. >> + */ >> +static void shutdown_one_device_async(void *data, async_cookie_t cookie) >> +{ >> + struct device *dev = data; >> + >> + async_synchronize_cookie_domain(dev->p->shutdown_after + 1, &sd_domain); >> + >> + shutdown_one_device(dev); >> +} >> + >> /** >> * device_shutdown - call ->shutdown() on each device to shutdown. >> */ >> void device_shutdown(void) >> { >> struct device *dev, *parent; >> + async_cookie_t cookie = 0; >> + struct device_link *link; >> + int idx; >> >> wait_for_device_probe(); >> device_block_probing(); >> @@ -4852,11 +4878,37 @@ void device_shutdown(void) >> list_del_init(&dev->kobj.entry); >> spin_unlock(&devices_kset->list_lock); >> >> - shutdown_one_device(dev); >> + >> + /* >> + * Set cookie for devices that will be shut down synchronously >> + */ >> + if (!dev->driver || !dev->driver->async_shutdown_enable) >> + dev->p->shutdown_after = cookie; >> + >> + get_device(dev); >> + get_device(parent); >> + >> + cookie = async_schedule_domain(shutdown_one_device_async, >> + dev, &sd_domain); >> + /* >> + * Ensure parent & suppliers wait for this device to shut down >> + */ >> + if (parent) { >> + parent->p->shutdown_after = cookie; >> + put_device(parent); >> + } >> + >> + idx = device_links_read_lock(); >> + list_for_each_entry_rcu(link, &dev->links.suppliers, c_node, >> + device_links_read_lock_held()) >> + link->supplier->p->shutdown_after = cookie; > > This will not fly if a supplier registered after its consumer. As we are > walking the list backward, the supplier will now wait for something that > is coming later during shutdown if the affected devices are still doing > this synchronously (as almost all at this stage). This creates a > circular dependency. > > Seems to explain the reboot hang that I'm seeing on an embedded target > with a mailbox dev waiting for a remoteproc dev while the mailbox being > after the remoteproc in the list (thus first on shutting down). > > This resolves the issue for me so far, but I don't think we are done yet: > > list_for_each_entry_rcu(link, &dev->links.suppliers, c_node, > device_links_read_lock_held()) { > if (link->supplier->driver && > link->supplier->driver->async_shutdown_enable) > link->supplier->p->shutdown_after = cookie; > } > > I wonder if overwriting the supplier's shutdown_after unconditionally is > a good idea. A supplier may have multiple consumers - will we overwrite > in the right order then? And why do we now need this ordering when we > were so far shutting down suppliers while consumers were still up? > The devices_kset list should already be in the right order for shutting stuff down--i.e., parents and suppliers should be shutdown later as the device_shutdown loop goes through the devices. With async shutdown this loop still goes the devices_kset list in the same order it did before the patch, so my expectation was that any parents/suppliers would come later in the loop than any children/siblings, and it would update shutdown_after as it went to ensure that each device ended up with the cookie of the last child/consumer that it needed to wait for. However, I missed that the devices_kset list isn't always reordered when a devlink is added and a consumer isn't dependent on the supplier (see device_is_dependent()). I have a patch would address that, and add a sanity check in case any devices get in the list in the wrong order somehow: diff --git a/drivers/base/core.c b/drivers/base/core.c index b69b82da8837..52d64b419c01 100644 --- a/drivers/base/core.c +++ b/drivers/base/core.c @@ -4832,6 +4832,13 @@ static void shutdown_one_device_async(void *data, async_cookie_t cookie) { struct device *dev = data; + /* + * Sanity check to prevent shutdown hang in case a parent or supplier + * is in devices_kset list in the wrong order + */ + if (dev->p->shutdown_after > cookie) + dev->p->shutdown_after = cookie - 1; + async_synchronize_cookie_domain(dev->p->shutdown_after + 1, &sd_domain); shutdown_one_device(dev); @@ -4898,8 +4905,11 @@ void device_shutdown(void) idx = device_links_read_lock(); list_for_each_entry_rcu(link, &dev->links.suppliers, c_node, - device_links_read_lock_held()) + device_links_read_lock_held()) { + if (device_link_flag_is_sync_state_only(link->flags)) + continue; link->supplier->p->shutdown_after = cookie; + } device_links_read_unlock(idx); put_device(dev); I'll submit this shortly if nobody responds with any issues with this. Thank you! > Same overwrite question applies to setting shutdown_after in parents. > Don't we rather need a list for shutdown_after, at least once everything > is async? > > This needs to be thought through once more, I guess. > > Jan > >> + device_links_read_unlock(idx); >> + put_device(dev); >> >> spin_lock(&devices_kset->list_lock); >> } >> spin_unlock(&devices_kset->list_lock); >> + async_synchronize_full_domain(&sd_domain); >> } >> >> /* >> diff --git a/include/linux/device/driver.h b/include/linux/device/driver.h >> index 1fc8b68786de..2b6127faaa25 100644 >> --- a/include/linux/device/driver.h >> +++ b/include/linux/device/driver.h >> @@ -56,6 +56,7 @@ enum probe_type { >> * @mod_name: Used for built-in modules. >> * @suppress_bind_attrs: Disables bind/unbind via sysfs. >> * @probe_type: Type of the probe (synchronous or asynchronous) to use. >> + * @async_shutdown_enable: Enables devices to be shutdown asynchronously. >> * @of_match_table: The open firmware table. >> * @acpi_match_table: The ACPI match table. >> * @probe: Called to query the existence of a specific device, >> @@ -102,6 +103,7 @@ struct device_driver { >> >> bool suppress_bind_attrs; /* disables bind/unbind via sysfs */ >> enum probe_type probe_type; >> + bool async_shutdown_enable; >> >> const struct of_device_id *of_match_table; >> const struct acpi_device_id *acpi_match_table; >