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23 October 2021, 00:29:24 UTC
Revision 093e5840ae76f1082633503964d035f40ed0216d authored by Sebastian Andrzej Siewior on 21 December 2015, 17:17:10 UTC, committed by Ingo Molnar on 06 January 2016, 10:01:07 UTC 
sched/core: Reset task's lockless wake-queues on fork()
 
In the following commit:

  7675104990ed ("sched: Implement lockless wake-queues")

we gained lockless wake-queues.

The -RT kernel managed to lockup itself with those. There could be multiple
attempts for task X to enqueue it for a wakeup _even_ if task X is already
running.

The reason is that task X could be runnable but not yet on CPU. The the
task performing the wakeup did not leave the CPU it could performe
multiple wakeups.

With the proper timming task X could be running and enqueued for a
wakeup. If this happens while X is performing a fork() then its its
child will have a !NULL `wake_q` member copied.

This is not a problem as long as the child task does not participate in
lockless wakeups :)

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 7675104990ed ("sched: Implement lockless wake-queues")
Link: http://lkml.kernel.org/r/20151221171710.GA5499@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
1 parent be958bd
Raw File
Tip revision: 093e5840ae76f1082633503964d035f40ed0216d authored by Sebastian Andrzej Siewior on 21 December 2015, 17:17:10 UTC
sched/core: Reset task's lockless wake-queues on fork()
Tip revision: 093e584
show_mem.c 
/*
 * Generic show_mem() implementation
 *
 * Copyright (C) 2008 Johannes Weiner <hannes@saeurebad.de>
 * All code subject to the GPL version 2.
 */

#include <linux/mm.h>
#include <linux/quicklist.h>
#include <linux/cma.h>

void show_mem(unsigned int filter)
{
	pg_data_t *pgdat;
	unsigned long total = 0, reserved = 0, highmem = 0;

	printk("Mem-Info:\n");
	show_free_areas(filter);

	for_each_online_pgdat(pgdat) {
		unsigned long flags;
		int zoneid;

		pgdat_resize_lock(pgdat, &flags);
		for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
			struct zone *zone = &pgdat->node_zones[zoneid];
			if (!populated_zone(zone))
				continue;

			total += zone->present_pages;
			reserved += zone->present_pages - zone->managed_pages;

			if (is_highmem_idx(zoneid))
				highmem += zone->present_pages;
		}
		pgdat_resize_unlock(pgdat, &flags);
	}

	printk("%lu pages RAM\n", total);
	printk("%lu pages HighMem/MovableOnly\n", highmem);
	printk("%lu pages reserved\n", reserved);
#ifdef CONFIG_CMA
	printk("%lu pages cma reserved\n", totalcma_pages);
#endif
#ifdef CONFIG_QUICKLIST
	printk("%lu pages in pagetable cache\n",
		quicklist_total_size());
#endif
#ifdef CONFIG_MEMORY_FAILURE
	printk("%lu pages hwpoisoned\n", atomic_long_read(&num_poisoned_pages));
#endif
}
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