Commit 13e2e556 authored by Tejun Heo's avatar Tejun Heo
Browse files

workqueue: fix unbound workqueue attrs hashing / comparison 



29c91e99 ("workqueue: implement attribute-based unbound worker_pool
management") implemented attrs based worker_pool matching.  It tried
to avoid false negative when comparing cpumasks with custom hash
function; unfortunately, the hash and comparison functions fail to
ignore CPUs which are not possible.  It incorrectly assumed that
bitmap_copy() skips leftover bits in the last word of bitmap and
cpumask_equal() ignores impossible CPUs.

This patch updates attrs->cpumask handling such that impossible CPUs
are properly ignored.

* Hash and copy functions no longer do anything special.  They expect
  their callers to clear impossible CPUs.

* alloc_workqueue_attrs() initializes the cpumask to cpu_possible_mask
  instead of setting all bits and explicit cpumask_setall() for
  unbound_std_wq_attrs[] in init_workqueues() is dropped.

* apply_workqueue_attrs() is now responsible for ignoring impossible
  CPUs.  It makes a copy of @attrs and clears impossible CPUs before
  doing anything else.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent bc0caf09

kernel/workqueue.c

+22 −32
Original line number Diff line number Diff line
@@ -3302,7 +3302,7 @@ struct workqueue_attrs *alloc_workqueue_attrs(gfp_t gfp_mask) 
	if (!alloc_cpumask_var(&attrs->cpumask, gfp_mask))

		goto fail;



	cpumask_setall(attrs->cpumask);

	cpumask_copy(attrs->cpumask, cpu_possible_mask);

	return attrs;

fail:

	free_workqueue_attrs(attrs);
@@ -3316,33 +3316,14 @@ static void copy_workqueue_attrs(struct workqueue_attrs *to, 
	cpumask_copy(to->cpumask, from->cpumask);

}



/*

 * Hacky implementation of jhash of bitmaps which only considers the

 * specified number of bits.  We probably want a proper implementation in

 * include/linux/jhash.h.

 */

static u32 jhash_bitmap(const unsigned long *bitmap, int bits, u32 hash)

{

	int nr_longs = bits / BITS_PER_LONG;

	int nr_leftover = bits % BITS_PER_LONG;

	unsigned long leftover = 0;



	if (nr_longs)

		hash = jhash(bitmap, nr_longs * sizeof(long), hash);

	if (nr_leftover) {

		bitmap_copy(&leftover, bitmap + nr_longs, nr_leftover);

		hash = jhash(&leftover, sizeof(long), hash);

	}

	return hash;

}



/* hash value of the content of @attr */

static u32 wqattrs_hash(const struct workqueue_attrs *attrs)

{

	u32 hash = 0;



	hash = jhash_1word(attrs->nice, hash);

	hash = jhash_bitmap(cpumask_bits(attrs->cpumask), nr_cpu_ids, hash);

	hash = jhash(cpumask_bits(attrs->cpumask),

		     BITS_TO_LONGS(nr_cpumask_bits) * sizeof(long), hash);

	return hash;

}
@@ -3652,7 +3633,8 @@ static void init_and_link_pwq(struct pool_workqueue *pwq, 
int apply_workqueue_attrs(struct workqueue_struct *wq,

			  const struct workqueue_attrs *attrs)

{

	struct pool_workqueue *pwq, *last_pwq;

	struct workqueue_attrs *new_attrs;

	struct pool_workqueue *pwq = NULL, *last_pwq;

	struct worker_pool *pool;



	/* only unbound workqueues can change attributes */
@@ -3663,15 +3645,21 @@ int apply_workqueue_attrs(struct workqueue_struct *wq, 
	if (WARN_ON((wq->flags & __WQ_ORDERED) && !list_empty(&wq->pwqs)))

		return -EINVAL;



	/* make a copy of @attrs and sanitize it */

	new_attrs = alloc_workqueue_attrs(GFP_KERNEL);

	if (!new_attrs)

		goto enomem;



	copy_workqueue_attrs(new_attrs, attrs);

	cpumask_and(new_attrs->cpumask, new_attrs->cpumask, cpu_possible_mask);



	pwq = kmem_cache_zalloc(pwq_cache, GFP_KERNEL);

	if (!pwq)

		return -ENOMEM;

		goto enomem;



	pool = get_unbound_pool(attrs);

	if (!pool) {

		kmem_cache_free(pwq_cache, pwq);

		return -ENOMEM;

	}

	pool = get_unbound_pool(new_attrs);

	if (!pool)

		goto enomem;



	init_and_link_pwq(pwq, wq, pool, &last_pwq);

	if (last_pwq) {
@@ -3681,6 +3669,11 @@ int apply_workqueue_attrs(struct workqueue_struct *wq, 
	}



	return 0;



enomem:

	kmem_cache_free(pwq_cache, pwq);

	free_workqueue_attrs(new_attrs);

	return -ENOMEM;

}



static int alloc_and_link_pwqs(struct workqueue_struct *wq)
@@ -4450,10 +4443,7 @@ static int __init init_workqueues(void) 
		struct workqueue_attrs *attrs;



		BUG_ON(!(attrs = alloc_workqueue_attrs(GFP_KERNEL)));



		attrs->nice = std_nice[i];

		cpumask_setall(attrs->cpumask);



		unbound_std_wq_attrs[i] = attrs;

	}

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