From 8d056c48e486249e6487910b83e0f3be7c14acf7 Mon Sep 17 00:00:00 2001 From: "Srivatsa S. Bhat" Date: Mon, 23 Jun 2014 13:22:02 -0700 Subject: CPU hotplug, smp: flush any pending IPI callbacks before CPU offline There is a race between the CPU offline code (within stop-machine) and the smp-call-function code, which can lead to getting IPIs on the outgoing CPU, *after* it has gone offline. Specifically, this can happen when using smp_call_function_single_async() to send the IPI, since this API allows sending asynchronous IPIs from IRQ disabled contexts. The exact race condition is described below. During CPU offline, in stop-machine, we don't enforce any rule in the _DISABLE_IRQ stage, regarding the order in which the outgoing CPU and the other CPUs disable their local interrupts. Due to this, we can encounter a situation in which an IPI is sent by one of the other CPUs to the outgoing CPU (while it is *still* online), but the outgoing CPU ends up noticing it only *after* it has gone offline. CPU 1 CPU 2 (Online CPU) (CPU going offline) Enter _PREPARE stage Enter _PREPARE stage Enter _DISABLE_IRQ stage = Got a device interrupt, and | Didn't notice the IPI the interrupt handler sent an | since interrupts were IPI to CPU 2 using | disabled on this CPU. smp_call_function_single_async() | = Enter _DISABLE_IRQ stage Enter _RUN stage Enter _RUN stage = Busy loop with interrupts | Invoke take_cpu_down() disabled. | and take CPU 2 offline = Enter _EXIT stage Enter _EXIT stage Re-enable interrupts Re-enable interrupts The pending IPI is noted immediately, but alas, the CPU is offline at this point. This of course, makes the smp-call-function IPI handler code running on CPU 2 unhappy and it complains about "receiving an IPI on an offline CPU". One real example of the scenario on CPU 1 is the block layer's complete-request call-path: __blk_complete_request() [interrupt-handler] raise_blk_irq() smp_call_function_single_async() However, if we look closely, the block layer does check that the target CPU is online before firing the IPI. So in this case, it is actually the unfortunate ordering/timing of events in the stop-machine phase that leads to receiving IPIs after the target CPU has gone offline. In reality, getting a late IPI on an offline CPU is not too bad by itself (this can happen even due to hardware latencies in IPI send-receive). It is a bug only if the target CPU really went offline without executing all the callbacks queued on its list. (Note that a CPU is free to execute its pending smp-call-function callbacks in a batch, without waiting for the corresponding IPIs to arrive for each one of those callbacks). So, fixing this issue can be broken up into two parts: 1. Ensure that a CPU goes offline only after executing all the callbacks queued on it. 2. Modify the warning condition in the smp-call-function IPI handler code such that it warns only if an offline CPU got an IPI *and* that CPU had gone offline with callbacks still pending in its queue. Achieving part 1 is straight-forward - just flush (execute) all the queued callbacks on the outgoing CPU in the CPU_DYING stage[1], including those callbacks for which the source CPU's IPIs might not have been received on the outgoing CPU yet. Once we do this, an IPI that arrives late on the CPU going offline (either due to the race mentioned above, or due to hardware latencies) will be completely harmless, since the outgoing CPU would have executed all the queued callbacks before going offline. Overall, this fix (parts 1 and 2 put together) additionally guarantees that we will see a warning only when the *IPI-sender code* is buggy - that is, if it queues the callback _after_ the target CPU has gone offline. [1]. The CPU_DYING part needs a little more explanation: by the time we execute the CPU_DYING notifier callbacks, the CPU would have already been marked offline. But we want to flush out the pending callbacks at this stage, ignoring the fact that the CPU is offline. So restructure the IPI handler code so that we can by-pass the "is-cpu-offline?" check in this particular case. (Of course, the right solution here is to fix CPU hotplug to mark the CPU offline _after_ invoking the CPU_DYING notifiers, but this requires a lot of audit to ensure that this change doesn't break any existing code; hence lets go with the solution proposed above until that is done). [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Srivatsa S. Bhat Suggested-by: Frederic Weisbecker Cc: "Paul E. McKenney" Cc: Borislav Petkov Cc: Christoph Hellwig Cc: Frederic Weisbecker Cc: Gautham R Shenoy Cc: Ingo Molnar Cc: Mel Gorman Cc: Mike Galbraith Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Rafael J. Wysocki Cc: Rik van Riel Cc: Rusty Russell Cc: Steven Rostedt Cc: Tejun Heo Cc: Thomas Gleixner Tested-by: Sachin Kamat Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/smp.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 49 insertions(+), 8 deletions(-) (limited to 'kernel') diff --git a/kernel/smp.c b/kernel/smp.c index 306f8180b0d..80c33f8de14 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -29,6 +29,8 @@ static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_function_data, cfd_data); static DEFINE_PER_CPU_SHARED_ALIGNED(struct llist_head, call_single_queue); +static void flush_smp_call_function_queue(bool warn_cpu_offline); + static int hotplug_cfd(struct notifier_block *nfb, unsigned long action, void *hcpu) { @@ -51,12 +53,27 @@ hotplug_cfd(struct notifier_block *nfb, unsigned long action, void *hcpu) #ifdef CONFIG_HOTPLUG_CPU case CPU_UP_CANCELED: case CPU_UP_CANCELED_FROZEN: + /* Fall-through to the CPU_DEAD[_FROZEN] case. */ case CPU_DEAD: case CPU_DEAD_FROZEN: free_cpumask_var(cfd->cpumask); free_percpu(cfd->csd); break; + + case CPU_DYING: + case CPU_DYING_FROZEN: + /* + * The IPIs for the smp-call-function callbacks queued by other + * CPUs might arrive late, either due to hardware latencies or + * because this CPU disabled interrupts (inside stop-machine) + * before the IPIs were sent. So flush out any pending callbacks + * explicitly (without waiting for the IPIs to arrive), to + * ensure that the outgoing CPU doesn't go offline with work + * still pending. + */ + flush_smp_call_function_queue(false); + break; #endif }; @@ -177,23 +194,47 @@ static int generic_exec_single(int cpu, struct call_single_data *csd, return 0; } -/* - * Invoked by arch to handle an IPI for call function single. Must be - * called from the arch with interrupts disabled. +/** + * generic_smp_call_function_single_interrupt - Execute SMP IPI callbacks + * + * Invoked by arch to handle an IPI for call function single. + * Must be called with interrupts disabled. */ void generic_smp_call_function_single_interrupt(void) { + flush_smp_call_function_queue(true); +} + +/** + * flush_smp_call_function_queue - Flush pending smp-call-function callbacks + * + * @warn_cpu_offline: If set to 'true', warn if callbacks were queued on an + * offline CPU. Skip this check if set to 'false'. + * + * Flush any pending smp-call-function callbacks queued on this CPU. This is + * invoked by the generic IPI handler, as well as by a CPU about to go offline, + * to ensure that all pending IPI callbacks are run before it goes completely + * offline. + * + * Loop through the call_single_queue and run all the queued callbacks. + * Must be called with interrupts disabled. + */ +static void flush_smp_call_function_queue(bool warn_cpu_offline) +{ + struct llist_head *head; struct llist_node *entry; struct call_single_data *csd, *csd_next; static bool warned; - entry = llist_del_all(&__get_cpu_var(call_single_queue)); + WARN_ON(!irqs_disabled()); + + head = &__get_cpu_var(call_single_queue); + entry = llist_del_all(head); entry = llist_reverse_order(entry); - /* - * Shouldn't receive this interrupt on a cpu that is not yet online. - */ - if (unlikely(!cpu_online(smp_processor_id()) && !warned)) { + /* There shouldn't be any pending callbacks on an offline CPU. */ + if (unlikely(warn_cpu_offline && !cpu_online(smp_processor_id()) && + !warned && !llist_empty(head))) { warned = true; WARN(1, "IPI on offline CPU %d\n", smp_processor_id()); -- cgit v1.2.3-70-g09d2 From b3acc56bfe1287c6b666e80edc70b89eea2a1a80 Mon Sep 17 00:00:00 2001 From: Petr Tesarik Date: Mon, 23 Jun 2014 13:22:03 -0700 Subject: kexec: save PG_head_mask in VMCOREINFO To allow filtering of huge pages, makedumpfile must be able to identify them in the dump. This can be done by checking the appropriate page flag, so communicate its value to makedumpfile through the VMCOREINFO interface. There's only one small catch. Depending on how many page flags are available on a given architecture, this bit can be called PG_head or PG_compound. I sent a similar patch back in 2012, but Eric Biederman did not like using an #ifdef. So, this time I'm adding a common symbol (PG_head_mask) instead. See https://lkml.org/lkml/2012/11/28/91 for the previous version. Signed-off-by: Petr Tesarik Acked-by: Vivek Goyal Cc: Eric Biederman Cc: Paul Mackerras Cc: Fengguang Wu Cc: Benjamin Herrenschmidt Cc: Shaohua Li Cc: Alexey Kardashevskiy Cc: Sasha Levin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/page-flags.h | 3 +++ kernel/kexec.c | 1 + 2 files changed, 4 insertions(+) (limited to 'kernel') diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 3c545b48aea..8304959ad33 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -360,6 +360,9 @@ static inline void ClearPageCompound(struct page *page) ClearPageHead(page); } #endif + +#define PG_head_mask ((1L << PG_head)) + #else /* * Reduce page flag use as much as possible by overlapping diff --git a/kernel/kexec.c b/kernel/kexec.c index 6748688813d..369f41a9412 100644 --- a/kernel/kexec.c +++ b/kernel/kexec.c @@ -1617,6 +1617,7 @@ static int __init crash_save_vmcoreinfo_init(void) #ifdef CONFIG_MEMORY_FAILURE VMCOREINFO_NUMBER(PG_hwpoison); #endif + VMCOREINFO_NUMBER(PG_head_mask); VMCOREINFO_NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE); arch_crash_save_vmcoreinfo(); -- cgit v1.2.3-70-g09d2 From bde92cf455a03a91badb7046855592d8c008e929 Mon Sep 17 00:00:00 2001 From: Don Zickus Date: Mon, 23 Jun 2014 13:22:03 -0700 Subject: kernel/watchdog.c: remove preemption restrictions when restarting lockup detector Peter Wu noticed the following splat on his machine when updating /proc/sys/kernel/watchdog_thresh: BUG: sleeping function called from invalid context at mm/slub.c:965 in_atomic(): 1, irqs_disabled(): 0, pid: 1, name: init 3 locks held by init/1: #0: (sb_writers#3){.+.+.+}, at: [] vfs_write+0x143/0x180 #1: (watchdog_proc_mutex){+.+.+.}, at: [] proc_dowatchdog+0x33/0x110 #2: (cpu_hotplug.lock){.+.+.+}, at: [] get_online_cpus+0x32/0x80 Preemption disabled at:[] proc_dowatchdog+0xe4/0x110 CPU: 0 PID: 1 Comm: init Not tainted 3.16.0-rc1-testing #34 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 Call Trace: dump_stack+0x4e/0x7a __might_sleep+0x11d/0x190 kmem_cache_alloc_trace+0x4e/0x1e0 perf_event_alloc+0x55/0x440 perf_event_create_kernel_counter+0x26/0xe0 watchdog_nmi_enable+0x75/0x140 update_timers_all_cpus+0x53/0xa0 proc_dowatchdog+0xe4/0x110 proc_sys_call_handler+0xb3/0xc0 proc_sys_write+0x14/0x20 vfs_write+0xad/0x180 SyS_write+0x49/0xb0 system_call_fastpath+0x16/0x1b NMI watchdog: disabled (cpu0): hardware events not enabled What happened is after updating the watchdog_thresh, the lockup detector is restarted to utilize the new value. Part of this process involved disabling preemption. Once preemption was disabled, perf tried to allocate a new event (as part of the restart). This caused the above BUG_ON as you can't sleep with preemption disabled. The preemption restriction seemed agressive as we are not doing anything on that particular cpu, but with all the online cpus (which are protected by the get_online_cpus lock). Remove the restriction and the BUG_ON goes away. Signed-off-by: Don Zickus Acked-by: Michal Hocko Reported-by: Peter Wu Tested-by: Peter Wu Acked-by: David Rientjes Cc: [3.13+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/watchdog.c | 2 -- 1 file changed, 2 deletions(-) (limited to 'kernel') diff --git a/kernel/watchdog.c b/kernel/watchdog.c index 516203e665f..30e482240da 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -527,10 +527,8 @@ static void update_timers_all_cpus(void) int cpu; get_online_cpus(); - preempt_disable(); for_each_online_cpu(cpu) update_timers(cpu); - preempt_enable(); put_online_cpus(); } -- cgit v1.2.3-70-g09d2 From 7cd2b0a34ab8e4db971920eef8982f985441adfb Mon Sep 17 00:00:00 2001 From: David Rientjes Date: Mon, 23 Jun 2014 13:22:04 -0700 Subject: mm, pcp: allow restoring percpu_pagelist_fraction default Oleg reports a division by zero error on zero-length write() to the percpu_pagelist_fraction sysctl: divide error: 0000 [#1] SMP DEBUG_PAGEALLOC CPU: 1 PID: 9142 Comm: badarea_io Not tainted 3.15.0-rc2-vm-nfs+ #19 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 task: ffff8800d5aeb6e0 ti: ffff8800d87a2000 task.ti: ffff8800d87a2000 RIP: 0010: percpu_pagelist_fraction_sysctl_handler+0x84/0x120 RSP: 0018:ffff8800d87a3e78 EFLAGS: 00010246 RAX: 0000000000000f89 RBX: ffff88011f7fd000 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000010 RBP: ffff8800d87a3e98 R08: ffffffff81d002c8 R09: ffff8800d87a3f50 R10: 000000000000000b R11: 0000000000000246 R12: 0000000000000060 R13: ffffffff81c3c3e0 R14: ffffffff81cfddf8 R15: ffff8801193b0800 FS: 00007f614f1e9740(0000) GS:ffff88011f440000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: 00007f614f1fa000 CR3: 00000000d9291000 CR4: 00000000000006e0 Call Trace: proc_sys_call_handler+0xb3/0xc0 proc_sys_write+0x14/0x20 vfs_write+0xba/0x1e0 SyS_write+0x46/0xb0 tracesys+0xe1/0xe6 However, if the percpu_pagelist_fraction sysctl is set by the user, it is also impossible to restore it to the kernel default since the user cannot write 0 to the sysctl. This patch allows the user to write 0 to restore the default behavior. It still requires a fraction equal to or larger than 8, however, as stated by the documentation for sanity. If a value in the range [1, 7] is written, the sysctl will return EINVAL. This successfully solves the divide by zero issue at the same time. Signed-off-by: David Rientjes Reported-by: Oleg Drokin Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/sysctl/vm.txt | 3 ++- kernel/sysctl.c | 3 +-- mm/page_alloc.c | 40 ++++++++++++++++++++++++++++------------ 3 files changed, 31 insertions(+), 15 deletions(-) (limited to 'kernel') diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt index bd4b34c0373..4415aa91568 100644 --- a/Documentation/sysctl/vm.txt +++ b/Documentation/sysctl/vm.txt @@ -702,7 +702,8 @@ The batch value of each per cpu pagelist is also updated as a result. It is set to pcp->high/4. The upper limit of batch is (PAGE_SHIFT * 8) The initial value is zero. Kernel does not use this value at boot time to set -the high water marks for each per cpu page list. +the high water marks for each per cpu page list. If the user writes '0' to this +sysctl, it will revert to this default behavior. ============================================================== diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 7de6555cfea..075d1903138 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -136,7 +136,6 @@ static unsigned long dirty_bytes_min = 2 * PAGE_SIZE; /* this is needed for the proc_dointvec_minmax for [fs_]overflow UID and GID */ static int maxolduid = 65535; static int minolduid; -static int min_percpu_pagelist_fract = 8; static int ngroups_max = NGROUPS_MAX; static const int cap_last_cap = CAP_LAST_CAP; @@ -1317,7 +1316,7 @@ static struct ctl_table vm_table[] = { .maxlen = sizeof(percpu_pagelist_fraction), .mode = 0644, .proc_handler = percpu_pagelist_fraction_sysctl_handler, - .extra1 = &min_percpu_pagelist_fract, + .extra1 = &zero, }, #ifdef CONFIG_MMU { diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 4f59fa29eda..20d17f8266f 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -69,6 +69,7 @@ /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */ static DEFINE_MUTEX(pcp_batch_high_lock); +#define MIN_PERCPU_PAGELIST_FRACTION (8) #ifdef CONFIG_USE_PERCPU_NUMA_NODE_ID DEFINE_PER_CPU(int, numa_node); @@ -4145,7 +4146,7 @@ static void __meminit zone_init_free_lists(struct zone *zone) memmap_init_zone((size), (nid), (zone), (start_pfn), MEMMAP_EARLY) #endif -static int __meminit zone_batchsize(struct zone *zone) +static int zone_batchsize(struct zone *zone) { #ifdef CONFIG_MMU int batch; @@ -4261,8 +4262,8 @@ static void pageset_set_high(struct per_cpu_pageset *p, pageset_update(&p->pcp, high, batch); } -static void __meminit pageset_set_high_and_batch(struct zone *zone, - struct per_cpu_pageset *pcp) +static void pageset_set_high_and_batch(struct zone *zone, + struct per_cpu_pageset *pcp) { if (percpu_pagelist_fraction) pageset_set_high(pcp, @@ -5881,23 +5882,38 @@ int percpu_pagelist_fraction_sysctl_handler(struct ctl_table *table, int write, void __user *buffer, size_t *length, loff_t *ppos) { struct zone *zone; - unsigned int cpu; + int old_percpu_pagelist_fraction; int ret; + mutex_lock(&pcp_batch_high_lock); + old_percpu_pagelist_fraction = percpu_pagelist_fraction; + ret = proc_dointvec_minmax(table, write, buffer, length, ppos); - if (!write || (ret < 0)) - return ret; + if (!write || ret < 0) + goto out; + + /* Sanity checking to avoid pcp imbalance */ + if (percpu_pagelist_fraction && + percpu_pagelist_fraction < MIN_PERCPU_PAGELIST_FRACTION) { + percpu_pagelist_fraction = old_percpu_pagelist_fraction; + ret = -EINVAL; + goto out; + } + + /* No change? */ + if (percpu_pagelist_fraction == old_percpu_pagelist_fraction) + goto out; - mutex_lock(&pcp_batch_high_lock); for_each_populated_zone(zone) { - unsigned long high; - high = zone->managed_pages / percpu_pagelist_fraction; + unsigned int cpu; + for_each_possible_cpu(cpu) - pageset_set_high(per_cpu_ptr(zone->pageset, cpu), - high); + pageset_set_high_and_batch(zone, + per_cpu_ptr(zone->pageset, cpu)); } +out: mutex_unlock(&pcp_batch_high_lock); - return 0; + return ret; } int hashdist = HASHDIST_DEFAULT; -- cgit v1.2.3-70-g09d2 From ed235875e2ca983197831337a986f0517074e1a0 Mon Sep 17 00:00:00 2001 From: Aaron Tomlin Date: Mon, 23 Jun 2014 13:22:05 -0700 Subject: kernel/watchdog.c: print traces for all cpus on lockup detection A 'softlockup' is defined as a bug that causes the kernel to loop in kernel mode for more than a predefined period to time, without giving other tasks a chance to run. Currently, upon detection of this condition by the per-cpu watchdog task, debug information (including a stack trace) is sent to the system log. On some occasions, we have observed that the "victim" rather than the actual "culprit" (i.e. the owner/holder of the contended resource) is reported to the user. Often this information has proven to be insufficient to assist debugging efforts. To avoid loss of useful debug information, for architectures which support NMI, this patch makes it possible to improve soft lockup reporting. This is accomplished by issuing an NMI to each cpu to obtain a stack trace. If NMI is not supported we just revert back to the old method. A sysctl and boot-time parameter is available to toggle this feature. [dzickus@redhat.com: add CONFIG_SMP in certain areas] [akpm@linux-foundation.org: additional CONFIG_SMP=n optimisations] [mq@suse.cz: fix warning] Signed-off-by: Aaron Tomlin Signed-off-by: Don Zickus Cc: David S. Miller Cc: Mateusz Guzik Cc: Oleg Nesterov Signed-off-by: Jan Moskyto Matejka Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/kernel-parameters.txt | 5 +++++ Documentation/sysctl/kernel.txt | 17 ++++++++++++++++ include/linux/nmi.h | 1 + kernel/sysctl.c | 11 +++++++++++ kernel/watchdog.c | 39 +++++++++++++++++++++++++++++++++++++ 5 files changed, 73 insertions(+) (limited to 'kernel') diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 884904975d0..c1b9aa8c5a5 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -3130,6 +3130,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted. [KNL] Should the soft-lockup detector generate panics. Format: + softlockup_all_cpu_backtrace= + [KNL] Should the soft-lockup detector generate + backtraces on all cpus. + Format: + sonypi.*= [HW] Sony Programmable I/O Control Device driver See Documentation/laptops/sonypi.txt diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt index 708bb7f1b7e..c14374e7177 100644 --- a/Documentation/sysctl/kernel.txt +++ b/Documentation/sysctl/kernel.txt @@ -75,6 +75,7 @@ show up in /proc/sys/kernel: - shmall - shmmax [ sysv ipc ] - shmmni +- softlockup_all_cpu_backtrace - stop-a [ SPARC only ] - sysrq ==> Documentation/sysrq.txt - sysctl_writes_strict @@ -783,6 +784,22 @@ via the /proc/sys interface: ============================================================== +softlockup_all_cpu_backtrace: + +This value controls the soft lockup detector thread's behavior +when a soft lockup condition is detected as to whether or not +to gather further debug information. If enabled, each cpu will +be issued an NMI and instructed to capture stack trace. + +This feature is only applicable for architectures which support +NMI. + +0: do nothing. This is the default behavior. + +1: on detection capture more debug information. + +============================================================== + tainted: Non-zero if the kernel has been tainted. Numeric values, which diff --git a/include/linux/nmi.h b/include/linux/nmi.h index a17ab6398d7..447775ee2c4 100644 --- a/include/linux/nmi.h +++ b/include/linux/nmi.h @@ -57,6 +57,7 @@ int hw_nmi_is_cpu_stuck(struct pt_regs *); u64 hw_nmi_get_sample_period(int watchdog_thresh); extern int watchdog_user_enabled; extern int watchdog_thresh; +extern int sysctl_softlockup_all_cpu_backtrace; struct ctl_table; extern int proc_dowatchdog(struct ctl_table *, int , void __user *, size_t *, loff_t *); diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 075d1903138..75b22e22a72 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -860,6 +860,17 @@ static struct ctl_table kern_table[] = { .extra1 = &zero, .extra2 = &one, }, +#ifdef CONFIG_SMP + { + .procname = "softlockup_all_cpu_backtrace", + .data = &sysctl_softlockup_all_cpu_backtrace, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = &zero, + .extra2 = &one, + }, +#endif /* CONFIG_SMP */ { .procname = "nmi_watchdog", .data = &watchdog_user_enabled, diff --git a/kernel/watchdog.c b/kernel/watchdog.c index 30e482240da..c3319bd1b04 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -31,6 +31,12 @@ int watchdog_user_enabled = 1; int __read_mostly watchdog_thresh = 10; +#ifdef CONFIG_SMP +int __read_mostly sysctl_softlockup_all_cpu_backtrace; +#else +#define sysctl_softlockup_all_cpu_backtrace 0 +#endif + static int __read_mostly watchdog_running; static u64 __read_mostly sample_period; @@ -47,6 +53,7 @@ static DEFINE_PER_CPU(bool, watchdog_nmi_touch); static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved); static DEFINE_PER_CPU(struct perf_event *, watchdog_ev); #endif +static unsigned long soft_lockup_nmi_warn; /* boot commands */ /* @@ -95,6 +102,15 @@ static int __init nosoftlockup_setup(char *str) } __setup("nosoftlockup", nosoftlockup_setup); /* */ +#ifdef CONFIG_SMP +static int __init softlockup_all_cpu_backtrace_setup(char *str) +{ + sysctl_softlockup_all_cpu_backtrace = + !!simple_strtol(str, NULL, 0); + return 1; +} +__setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup); +#endif /* * Hard-lockup warnings should be triggered after just a few seconds. Soft- @@ -271,6 +287,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts); struct pt_regs *regs = get_irq_regs(); int duration; + int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace; /* kick the hardlockup detector */ watchdog_interrupt_count(); @@ -317,6 +334,17 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) if (__this_cpu_read(soft_watchdog_warn) == true) return HRTIMER_RESTART; + if (softlockup_all_cpu_backtrace) { + /* Prevent multiple soft-lockup reports if one cpu is already + * engaged in dumping cpu back traces + */ + if (test_and_set_bit(0, &soft_lockup_nmi_warn)) { + /* Someone else will report us. Let's give up */ + __this_cpu_write(soft_watchdog_warn, true); + return HRTIMER_RESTART; + } + } + printk(KERN_EMERG "BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n", smp_processor_id(), duration, current->comm, task_pid_nr(current)); @@ -327,6 +355,17 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) else dump_stack(); + if (softlockup_all_cpu_backtrace) { + /* Avoid generating two back traces for current + * given that one is already made above + */ + trigger_allbutself_cpu_backtrace(); + + clear_bit(0, &soft_lockup_nmi_warn); + /* Barrier to sync with other cpus */ + smp_mb__after_atomic(); + } + if (softlockup_panic) panic("softlockup: hung tasks"); __this_cpu_write(soft_watchdog_warn, true); -- cgit v1.2.3-70-g09d2