* [PATCH 2/2] workqueue: fix unbound workqueue attrs hashing / comparison
2013-03-28 6:29 [PATCH 1/2] workqueue: fix race condition in unbound workqueue free path Tejun Heo
@ 2013-03-28 6:30 ` Tejun Heo
2013-03-28 6:31 ` [PATCH 1/2] workqueue: fix race condition in unbound workqueue free path Tejun Heo
1 sibling, 0 replies; 4+ messages in thread
From: Tejun Heo @ 2013-03-28 6:30 UTC (permalink / raw)
To: linux-kernel, Lai Jiangshan
>From b37c3e3a74346749f0278c349dc0857107cb4370 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Wed, 27 Mar 2013 23:27:41 -0700
29c91e9912b ("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: Tejun Heo <tj@kernel.org>
---
kernel/workqueue.c | 54 ++++++++++++++++++++++--------------------------------
1 file changed, 22 insertions(+), 32 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 4d34432..abe1f0d 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -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;
}
--
1.8.1.4
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