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Date:   Thu, 17 Jan 2019 11:51:46 +0800
From:   fei phung <feiphung27@...il.com>
To:     mst@...hat.com, feiphung@...mail.com, netdev@...r.kernel.org
Subject: Re: Question on ptr_ring linux header

Hi,

I am having data race from threadsanitizer report.

Could you see if there is still data race in the following code using
ptr_ring API ?



/*
 * Filename: circ_ring.c
 * Version: 1.0
 * Description: A circular buffer using API from
 * https://github.com/torvalds/linux/blob/master/include/linux/ptr_ring.h
 */

#include <linux/slab.h>
#include <linux/mm.h>
#include <linux/ptr_ring.h>
#include "circ_ring.h"
//#include <assert.h>

#define DEBUG 1

#ifdef DEBUG
#define DEBUG_MSG(...) printk(__VA_ARGS__)
#else
#define DEBUG_MSG(...)
#endif

struct ptr_ring * init_circ_queue(int len)
{
    struct ptr_ring * q;

    q = kzalloc(sizeof(struct ptr_ring), GFP_KERNEL);
    if (q == NULL) {
        DEBUG_MSG(KERN_ERR "Not enough memory to allocate ptr_ring");
        return NULL;
    }

    // creates an array of length 'len' where each array location can
store a struct * item
    if(ptr_ring_init(q, len, GFP_KERNEL) != 0) {
        DEBUG_MSG(KERN_ERR "Not enough memory to allocate ptr_ring array");
        return NULL;
    }

    return q;
}

inline int push_circ_queue(struct ptr_ring * buffer, struct item * item_push)
{
    /* insert one item into the buffer */
    if(ptr_ring_produce_any(buffer, item_push) == 0) // operation is successful
    {
        DEBUG_MSG(KERN_INFO "Successfully pushed val1 = %u and val2 =
%u\n", item_push->val1, item_push->val2);

        return 0;
    }

    else {
        DEBUG_MSG(KERN_INFO "full, not enough buffer space\n");

        return 1;
    }
}

inline int pop_circ_queue(struct ptr_ring * buffer, struct item * item_pop)
{
    struct item * item_temp = 0;

    /* extract one item struct containing two unsigned integers from
the buffer */
    item_temp = (struct item *)ptr_ring_consume_any(buffer);

    if(item_temp) // (!= NULL)
    {
        item_pop->val1 = item_temp->val1;
        item_pop->val2 = item_temp->val2;

    // val1 will never be zero since the event number starts from 1
(so, val1 in push_circ_queue() will not be zero, same case after
pop_circ_queue()), and 0 is only possible during initialization, not
during pop_circ_queue()
        //assert(item_pop->val1 != 0);

        DEBUG_MSG(KERN_INFO "Before pop, head = %u , tail = %u\n",
buffer->consumer_head, buffer->consumer_tail);

        DEBUG_MSG(KERN_INFO "val1 = %u , val2 = %u\n", item_pop->val1,
item_pop->val2);

        DEBUG_MSG(KERN_INFO "After pop, head = %u , tail = %u\n",
buffer->consumer_head, buffer->consumer_tail);

        return 0;
    }

    else {
        //DEBUG_MSG(KERN_INFO "empty, nothing to pop from the ring\n");

        return 1;
    }
}

void free_circ_queue(struct ptr_ring * q)
{
    ptr_ring_cleanup(q, NULL);
}



Regards,
Phung

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