Revision 03049269de433cb5fe2859be9ae4469ceb1163ed authored by Michal Hocko on 25 March 2016, 21:20:33 UTC, committed by Linus Torvalds on 25 March 2016, 23:37:42 UTC
wake_oom_reaper has allowed only 1 oom victim to be queued. The main reason for that was the simplicity as other solutions would require some way of queuing. The current approach is racy and that was deemed sufficient as the oom_reaper is considered a best effort approach to help with oom handling when the OOM victim cannot terminate in a reasonable time. The race could lead to missing an oom victim which can get stuck out_of_memory wake_oom_reaper cmpxchg // OK oom_reaper oom_reap_task __oom_reap_task oom_victim terminates atomic_inc_not_zero // fail out_of_memory wake_oom_reaper cmpxchg // fails task_to_reap = NULL This race requires 2 OOM invocations in a short time period which is not very likely but certainly not impossible. E.g. the original victim might have not released a lot of memory for some reason. The situation would improve considerably if wake_oom_reaper used a more robust queuing. This is what this patch implements. This means adding oom_reaper_list list_head into task_struct (eat a hole before embeded thread_struct for that purpose) and a oom_reaper_lock spinlock for queuing synchronization. wake_oom_reaper will then add the task on the queue and oom_reaper will dequeue it. Signed-off-by: Michal Hocko <mhocko@suse.com> Cc: Vladimir Davydov <vdavydov@virtuozzo.com> Cc: Andrea Argangeli <andrea@kernel.org> Cc: David Rientjes <rientjes@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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nmi_backtrace.c
/*
* NMI backtrace support
*
* Gratuitously copied from arch/x86/kernel/apic/hw_nmi.c by Russell King,
* with the following header:
*
* HW NMI watchdog support
*
* started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
*
* Arch specific calls to support NMI watchdog
*
* Bits copied from original nmi.c file
*/
#include <linux/cpumask.h>
#include <linux/delay.h>
#include <linux/kprobes.h>
#include <linux/nmi.h>
#include <linux/seq_buf.h>
#ifdef arch_trigger_all_cpu_backtrace
/* For reliability, we're prepared to waste bits here. */
static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
static cpumask_t printtrace_mask;
#define NMI_BUF_SIZE 4096
struct nmi_seq_buf {
unsigned char buffer[NMI_BUF_SIZE];
struct seq_buf seq;
};
/* Safe printing in NMI context */
static DEFINE_PER_CPU(struct nmi_seq_buf, nmi_print_seq);
/* "in progress" flag of arch_trigger_all_cpu_backtrace */
static unsigned long backtrace_flag;
static void print_seq_line(struct nmi_seq_buf *s, int start, int end)
{
const char *buf = s->buffer + start;
printk("%.*s", (end - start) + 1, buf);
}
/*
* When raise() is called it will be is passed a pointer to the
* backtrace_mask. Architectures that call nmi_cpu_backtrace()
* directly from their raise() functions may rely on the mask
* they are passed being updated as a side effect of this call.
*/
void nmi_trigger_all_cpu_backtrace(bool include_self,
void (*raise)(cpumask_t *mask))
{
struct nmi_seq_buf *s;
int i, cpu, this_cpu = get_cpu();
if (test_and_set_bit(0, &backtrace_flag)) {
/*
* If there is already a trigger_all_cpu_backtrace() in progress
* (backtrace_flag == 1), don't output double cpu dump infos.
*/
put_cpu();
return;
}
cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask);
if (!include_self)
cpumask_clear_cpu(this_cpu, to_cpumask(backtrace_mask));
cpumask_copy(&printtrace_mask, to_cpumask(backtrace_mask));
/*
* Set up per_cpu seq_buf buffers that the NMIs running on the other
* CPUs will write to.
*/
for_each_cpu(cpu, to_cpumask(backtrace_mask)) {
s = &per_cpu(nmi_print_seq, cpu);
seq_buf_init(&s->seq, s->buffer, NMI_BUF_SIZE);
}
if (!cpumask_empty(to_cpumask(backtrace_mask))) {
pr_info("Sending NMI to %s CPUs:\n",
(include_self ? "all" : "other"));
raise(to_cpumask(backtrace_mask));
}
/* Wait for up to 10 seconds for all CPUs to do the backtrace */
for (i = 0; i < 10 * 1000; i++) {
if (cpumask_empty(to_cpumask(backtrace_mask)))
break;
mdelay(1);
touch_softlockup_watchdog();
}
/*
* Now that all the NMIs have triggered, we can dump out their
* back traces safely to the console.
*/
for_each_cpu(cpu, &printtrace_mask) {
int len, last_i = 0;
s = &per_cpu(nmi_print_seq, cpu);
len = seq_buf_used(&s->seq);
if (!len)
continue;
/* Print line by line. */
for (i = 0; i < len; i++) {
if (s->buffer[i] == '\n') {
print_seq_line(s, last_i, i);
last_i = i + 1;
}
}
/* Check if there was a partial line. */
if (last_i < len) {
print_seq_line(s, last_i, len - 1);
pr_cont("\n");
}
}
clear_bit(0, &backtrace_flag);
smp_mb__after_atomic();
put_cpu();
}
/*
* It is not safe to call printk() directly from NMI handlers.
* It may be fine if the NMI detected a lock up and we have no choice
* but to do so, but doing a NMI on all other CPUs to get a back trace
* can be done with a sysrq-l. We don't want that to lock up, which
* can happen if the NMI interrupts a printk in progress.
*
* Instead, we redirect the vprintk() to this nmi_vprintk() that writes
* the content into a per cpu seq_buf buffer. Then when the NMIs are
* all done, we can safely dump the contents of the seq_buf to a printk()
* from a non NMI context.
*/
static int nmi_vprintk(const char *fmt, va_list args)
{
struct nmi_seq_buf *s = this_cpu_ptr(&nmi_print_seq);
unsigned int len = seq_buf_used(&s->seq);
seq_buf_vprintf(&s->seq, fmt, args);
return seq_buf_used(&s->seq) - len;
}
bool nmi_cpu_backtrace(struct pt_regs *regs)
{
int cpu = smp_processor_id();
if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
printk_func_t printk_func_save = this_cpu_read(printk_func);
/* Replace printk to write into the NMI seq */
this_cpu_write(printk_func, nmi_vprintk);
pr_warn("NMI backtrace for cpu %d\n", cpu);
if (regs)
show_regs(regs);
else
dump_stack();
this_cpu_write(printk_func, printk_func_save);
cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
return true;
}
return false;
}
NOKPROBE_SYMBOL(nmi_cpu_backtrace);
#endif
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