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67d6212afd
This reverts commit774a1221e8
. We need to finish all async code before the module init sequence is done. In the reverted commit the PF_USED_ASYNC flag was added to mark a thread that called async_schedule(). Then the PF_USED_ASYNC flag was used to determine whether or not async_synchronize_full() needs to be invoked. This works when modprobe thread is calling async_schedule(), but it does not work if module dispatches init code to a worker thread which then calls async_schedule(). For example, PCI driver probing is invoked from a worker thread based on a node where device is attached: if (cpu < nr_cpu_ids) error = work_on_cpu(cpu, local_pci_probe, &ddi); else error = local_pci_probe(&ddi); We end up in a situation where a worker thread gets the PF_USED_ASYNC flag set instead of the modprobe thread. As a result, async_synchronize_full() is not invoked and modprobe completes without waiting for the async code to finish. The issue was discovered while loading the pm80xx driver: (scsi_mod.scan=async) modprobe pm80xx worker ... do_init_module() ... pci_call_probe() work_on_cpu(local_pci_probe) local_pci_probe() pm8001_pci_probe() scsi_scan_host() async_schedule() worker->flags |= PF_USED_ASYNC; ... < return from worker > ... if (current->flags & PF_USED_ASYNC) <--- false async_synchronize_full(); Commit21c3c5d280
("block: don't request module during elevator init") fixed the deadlock issue which the reverted commit774a1221e8
("module, async: async_synchronize_full() on module init iff async is used") tried to fix. Since commit0fdff3ec6d
("async, kmod: warn on synchronous request_module() from async workers") synchronous module loading from async is not allowed. Given that the original deadlock issue is fixed and it is no longer allowed to call synchronous request_module() from async we can remove PF_USED_ASYNC flag to make module init consistently invoke async_synchronize_full() unless async module probe is requested. Signed-off-by: Igor Pylypiv <ipylypiv@google.com> Reviewed-by: Changyuan Lyu <changyuanl@google.com> Reviewed-by: Luis Chamberlain <mcgrof@kernel.org> Acked-by: Tejun Heo <tj@kernel.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
306 lines
9.2 KiB
C
306 lines
9.2 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* async.c: Asynchronous function calls for boot performance
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*
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* (C) Copyright 2009 Intel Corporation
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* Author: Arjan van de Ven <arjan@linux.intel.com>
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*/
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/*
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Goals and Theory of Operation
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The primary goal of this feature is to reduce the kernel boot time,
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by doing various independent hardware delays and discovery operations
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decoupled and not strictly serialized.
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More specifically, the asynchronous function call concept allows
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certain operations (primarily during system boot) to happen
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asynchronously, out of order, while these operations still
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have their externally visible parts happen sequentially and in-order.
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(not unlike how out-of-order CPUs retire their instructions in order)
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Key to the asynchronous function call implementation is the concept of
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a "sequence cookie" (which, although it has an abstracted type, can be
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thought of as a monotonically incrementing number).
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The async core will assign each scheduled event such a sequence cookie and
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pass this to the called functions.
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The asynchronously called function should before doing a globally visible
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operation, such as registering device numbers, call the
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async_synchronize_cookie() function and pass in its own cookie. The
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async_synchronize_cookie() function will make sure that all asynchronous
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operations that were scheduled prior to the operation corresponding with the
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cookie have completed.
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Subsystem/driver initialization code that scheduled asynchronous probe
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functions, but which shares global resources with other drivers/subsystems
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that do not use the asynchronous call feature, need to do a full
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synchronization with the async_synchronize_full() function, before returning
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from their init function. This is to maintain strict ordering between the
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asynchronous and synchronous parts of the kernel.
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*/
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#include <linux/async.h>
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#include <linux/atomic.h>
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#include <linux/ktime.h>
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#include <linux/export.h>
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#include <linux/wait.h>
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#include <linux/sched.h>
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#include <linux/slab.h>
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#include <linux/workqueue.h>
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#include "workqueue_internal.h"
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static async_cookie_t next_cookie = 1;
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#define MAX_WORK 32768
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#define ASYNC_COOKIE_MAX ULLONG_MAX /* infinity cookie */
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static LIST_HEAD(async_global_pending); /* pending from all registered doms */
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static ASYNC_DOMAIN(async_dfl_domain);
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static DEFINE_SPINLOCK(async_lock);
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struct async_entry {
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struct list_head domain_list;
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struct list_head global_list;
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struct work_struct work;
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async_cookie_t cookie;
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async_func_t func;
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void *data;
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struct async_domain *domain;
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};
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static DECLARE_WAIT_QUEUE_HEAD(async_done);
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static atomic_t entry_count;
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static long long microseconds_since(ktime_t start)
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{
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ktime_t now = ktime_get();
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return ktime_to_ns(ktime_sub(now, start)) >> 10;
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}
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static async_cookie_t lowest_in_progress(struct async_domain *domain)
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{
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struct async_entry *first = NULL;
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async_cookie_t ret = ASYNC_COOKIE_MAX;
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unsigned long flags;
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spin_lock_irqsave(&async_lock, flags);
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if (domain) {
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if (!list_empty(&domain->pending))
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first = list_first_entry(&domain->pending,
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struct async_entry, domain_list);
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} else {
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if (!list_empty(&async_global_pending))
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first = list_first_entry(&async_global_pending,
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struct async_entry, global_list);
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}
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if (first)
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ret = first->cookie;
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spin_unlock_irqrestore(&async_lock, flags);
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return ret;
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}
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/*
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* pick the first pending entry and run it
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*/
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static void async_run_entry_fn(struct work_struct *work)
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{
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struct async_entry *entry =
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container_of(work, struct async_entry, work);
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unsigned long flags;
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ktime_t calltime;
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/* 1) run (and print duration) */
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pr_debug("calling %lli_%pS @ %i\n", (long long)entry->cookie,
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entry->func, task_pid_nr(current));
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calltime = ktime_get();
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entry->func(entry->data, entry->cookie);
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pr_debug("initcall %lli_%pS returned after %lld usecs\n",
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(long long)entry->cookie, entry->func,
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microseconds_since(calltime));
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/* 2) remove self from the pending queues */
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spin_lock_irqsave(&async_lock, flags);
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list_del_init(&entry->domain_list);
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list_del_init(&entry->global_list);
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/* 3) free the entry */
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kfree(entry);
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atomic_dec(&entry_count);
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spin_unlock_irqrestore(&async_lock, flags);
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/* 4) wake up any waiters */
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wake_up(&async_done);
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}
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/**
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* async_schedule_node_domain - NUMA specific version of async_schedule_domain
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* @func: function to execute asynchronously
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* @data: data pointer to pass to the function
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* @node: NUMA node that we want to schedule this on or close to
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* @domain: the domain
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*
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* Returns an async_cookie_t that may be used for checkpointing later.
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* @domain may be used in the async_synchronize_*_domain() functions to
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* wait within a certain synchronization domain rather than globally.
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*
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* Note: This function may be called from atomic or non-atomic contexts.
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*
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* The node requested will be honored on a best effort basis. If the node
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* has no CPUs associated with it then the work is distributed among all
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* available CPUs.
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*/
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async_cookie_t async_schedule_node_domain(async_func_t func, void *data,
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int node, struct async_domain *domain)
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{
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struct async_entry *entry;
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unsigned long flags;
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async_cookie_t newcookie;
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/* allow irq-off callers */
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entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
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/*
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* If we're out of memory or if there's too much work
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* pending already, we execute synchronously.
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*/
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if (!entry || atomic_read(&entry_count) > MAX_WORK) {
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kfree(entry);
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spin_lock_irqsave(&async_lock, flags);
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newcookie = next_cookie++;
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spin_unlock_irqrestore(&async_lock, flags);
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/* low on memory.. run synchronously */
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func(data, newcookie);
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return newcookie;
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}
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INIT_LIST_HEAD(&entry->domain_list);
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INIT_LIST_HEAD(&entry->global_list);
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INIT_WORK(&entry->work, async_run_entry_fn);
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entry->func = func;
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entry->data = data;
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entry->domain = domain;
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spin_lock_irqsave(&async_lock, flags);
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/* allocate cookie and queue */
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newcookie = entry->cookie = next_cookie++;
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list_add_tail(&entry->domain_list, &domain->pending);
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if (domain->registered)
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list_add_tail(&entry->global_list, &async_global_pending);
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atomic_inc(&entry_count);
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spin_unlock_irqrestore(&async_lock, flags);
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/* schedule for execution */
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queue_work_node(node, system_unbound_wq, &entry->work);
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return newcookie;
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}
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EXPORT_SYMBOL_GPL(async_schedule_node_domain);
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/**
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* async_schedule_node - NUMA specific version of async_schedule
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* @func: function to execute asynchronously
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* @data: data pointer to pass to the function
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* @node: NUMA node that we want to schedule this on or close to
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*
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* Returns an async_cookie_t that may be used for checkpointing later.
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* Note: This function may be called from atomic or non-atomic contexts.
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*
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* The node requested will be honored on a best effort basis. If the node
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* has no CPUs associated with it then the work is distributed among all
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* available CPUs.
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*/
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async_cookie_t async_schedule_node(async_func_t func, void *data, int node)
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{
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return async_schedule_node_domain(func, data, node, &async_dfl_domain);
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}
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EXPORT_SYMBOL_GPL(async_schedule_node);
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/**
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* async_synchronize_full - synchronize all asynchronous function calls
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*
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* This function waits until all asynchronous function calls have been done.
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*/
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void async_synchronize_full(void)
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{
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async_synchronize_full_domain(NULL);
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}
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EXPORT_SYMBOL_GPL(async_synchronize_full);
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/**
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* async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
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* @domain: the domain to synchronize
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*
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* This function waits until all asynchronous function calls for the
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* synchronization domain specified by @domain have been done.
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*/
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void async_synchronize_full_domain(struct async_domain *domain)
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{
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async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain);
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}
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EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
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/**
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* async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
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* @cookie: async_cookie_t to use as checkpoint
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* @domain: the domain to synchronize (%NULL for all registered domains)
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*
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* This function waits until all asynchronous function calls for the
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* synchronization domain specified by @domain submitted prior to @cookie
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* have been done.
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*/
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void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain)
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{
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ktime_t starttime;
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pr_debug("async_waiting @ %i\n", task_pid_nr(current));
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starttime = ktime_get();
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wait_event(async_done, lowest_in_progress(domain) >= cookie);
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pr_debug("async_continuing @ %i after %lli usec\n", task_pid_nr(current),
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microseconds_since(starttime));
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}
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EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
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/**
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* async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
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* @cookie: async_cookie_t to use as checkpoint
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*
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* This function waits until all asynchronous function calls prior to @cookie
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* have been done.
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*/
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void async_synchronize_cookie(async_cookie_t cookie)
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{
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async_synchronize_cookie_domain(cookie, &async_dfl_domain);
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}
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EXPORT_SYMBOL_GPL(async_synchronize_cookie);
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/**
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* current_is_async - is %current an async worker task?
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*
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* Returns %true if %current is an async worker task.
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*/
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bool current_is_async(void)
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{
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struct worker *worker = current_wq_worker();
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return worker && worker->current_func == async_run_entry_fn;
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}
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EXPORT_SYMBOL_GPL(current_is_async);
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