Messages in this thread | | | From | Laurent Pinchart <> | Subject | CMA: test_pages_isolated failures in alloc_contig_range | Date | Sun, 26 Oct 2014 23:09:16 +0200 |
| |
Hello,
I've run into a CMA-related issue while testing a DMA engine driver with dmatest on a Renesas R-Car ARM platform.
When allocating contiguous memory through CMA the kernel prints the following messages to the kernel log.
[ 99.770000] alloc_contig_range test_pages_isolated(6b843, 6b844) failed [ 124.220000] alloc_contig_range test_pages_isolated(6b843, 6b844) failed [ 127.550000] alloc_contig_range test_pages_isolated(6b845, 6b846) failed [ 132.850000] alloc_contig_range test_pages_isolated(6b845, 6b846) failed [ 151.390000] alloc_contig_range test_pages_isolated(6b843, 6b844) failed [ 166.490000] alloc_contig_range test_pages_isolated(6b843, 6b844) failed [ 181.450000] alloc_contig_range test_pages_isolated(6b845, 6b846) failed
I've stripped the dmatest module down as much as possible to remove any hardware dependencies and came up with the following implementation.
----------------------------------------------------------------------------- /* * CMA test module * * Copyright (C) 2014 Laurent Pinchart * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 as * published by the Free Software Foundation. */
#include <linux/delay.h> #include <linux/dma-mapping.h> #include <linux/freezer.h> #include <linux/kthread.h> #include <linux/module.h> #include <linux/moduleparam.h> #include <linux/slab.h> #include <linux/wait.h>
static unsigned int num_threads = 4; module_param(num_threads, uint, S_IRUGO | S_IWUSR);
static unsigned int iterations = 100000; module_param(iterations, uint, S_IRUGO | S_IWUSR);
struct cma_test_thread { struct list_head node; struct task_struct *task; bool done; };
static DECLARE_WAIT_QUEUE_HEAD(thread_wait); static LIST_HEAD(threads);
static int cma_test_thread(void *data) { struct cma_test_thread *thread = data; unsigned int i = 0;
set_freezable();
while (!kthread_should_stop() && i < iterations) { dma_addr_t dma; void *mem;
mem = dma_alloc_coherent(NULL, 32, &dma, GFP_KERNEL); usleep_range(1000, 2000); if (mem) dma_free_coherent(NULL, 32, mem, dma); else printk(KERN_INFO "allocation error @%u\n", i); ++i; }
thread->done = true; wake_up(&thread_wait);
return 0; }
static bool cma_test_threads_done(void) { struct cma_test_thread *thread;
list_for_each_entry(thread, &threads, node) { if (!thread->done) return false; }
return true; }
static int cma_test_init(void) { struct cma_test_thread *thread, *_thread; unsigned int i;
for (i = 0; i < num_threads; ++i) { thread = kzalloc(sizeof(*thread), GFP_KERNEL); if (!thread) { pr_warn("No memory for thread %u\n", i); break; }
thread->task = kthread_create(cma_test_thread, thread, "cmatest-%u", i); if (IS_ERR(thread->task)) { pr_warn("Failed to create thread %u\n", i); kfree(thread); break; }
get_task_struct(thread->task); list_add_tail(&thread->node, &threads); wake_up_process(thread->task); }
wait_event(thread_wait, cma_test_threads_done());
list_for_each_entry_safe(thread, _thread, &threads, node) { kthread_stop(thread->task); put_task_struct(thread->task); list_del(&thread->node); kfree(thread); }
return 0; } module_init(cma_test_init);
static void cma_test_exit(void) { } module_exit(cma_test_exit);
MODULE_AUTHOR("Laurent Pinchart"); MODULE_LICENSE("GPL v2"); -----------------------------------------------------------------------------
Loading the module will start 4 threads that will allocate and free DMA coherent memory in a tight loop and eventually produce the error. It seems like the probability of occurrence grows with the number of threads, which could indicate a race condition.
The tests have been run on 3.18-rc1, but previous tests on 3.16 did exhibit the same behaviour.
I'm not that familiar with the CMA internals, help would be appreciated to debug the problem.
-- Regards,
Laurent Pinchart
| |