workqueue: introduce WORK_OFFQ_CPU_NONE

Currently, when a work item is off queue, high bits of its data
encodes the last CPU it was on.  This is scheduled to be changed to
pool ID, which will make it impossible to use WORK_CPU_NONE to
indicate no association.

This patch limits the number of bits which are used for off-queue cpu
number to 31 (so that the max fits in an int) and uses the highest
possible value - WORK_OFFQ_CPU_NONE - to indicate no association.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index ff68b1d95b41716b908e626cf4d067c49b34c675..f8b35763e55fa07fa6036db11e5b0b01810805ed 100644 (file)
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -73,13 +73,21 @@ enum {
 
        WORK_OFFQ_CANCELING     = (1 << WORK_OFFQ_FLAG_BASE),
 
+       /*
+        * When a work item is off queue, its high bits point to the last
+        * cpu it was on.  Cap at 31 bits and use the highest number to
+        * indicate that no cpu is associated.
+        */
        WORK_OFFQ_FLAG_BITS     = 1,
        WORK_OFFQ_CPU_SHIFT     = WORK_OFFQ_FLAG_BASE + WORK_OFFQ_FLAG_BITS,
+       WORK_OFFQ_LEFT          = BITS_PER_LONG - WORK_OFFQ_CPU_SHIFT,
+       WORK_OFFQ_CPU_BITS      = WORK_OFFQ_LEFT <= 31 ? WORK_OFFQ_LEFT : 31,
+       WORK_OFFQ_CPU_NONE      = (1LU << WORK_OFFQ_CPU_BITS) - 1,
 
        /* convenience constants */
        WORK_STRUCT_FLAG_MASK   = (1UL << WORK_STRUCT_FLAG_BITS) - 1,
        WORK_STRUCT_WQ_DATA_MASK = ~WORK_STRUCT_FLAG_MASK,
-       WORK_STRUCT_NO_CPU      = (unsigned long)WORK_CPU_NONE << WORK_OFFQ_CPU_SHIFT,
+       WORK_STRUCT_NO_CPU      = (unsigned long)WORK_OFFQ_CPU_NONE << WORK_OFFQ_CPU_SHIFT,
 
        /* bit mask for work_busy() return values */
        WORK_BUSY_PENDING       = 1 << 0,

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 1a686e481132a9cbab472f0fefb95608960cf5de..405282d30046a2146576d77b4503d5d06852b7dc 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -573,7 +573,7 @@ static struct global_cwq *get_work_gcwq(struct work_struct *work)
                        (data & WORK_STRUCT_WQ_DATA_MASK))->pool->gcwq;
 
        cpu = data >> WORK_OFFQ_CPU_SHIFT;
-       if (cpu == WORK_CPU_NONE)
+       if (cpu == WORK_OFFQ_CPU_NONE)
                return NULL;
 
        BUG_ON(cpu >= nr_cpu_ids && cpu != WORK_CPU_UNBOUND);
@@ -583,7 +583,7 @@ static struct global_cwq *get_work_gcwq(struct work_struct *work)
 static void mark_work_canceling(struct work_struct *work)
 {
        struct global_cwq *gcwq = get_work_gcwq(work);
-       unsigned long cpu = gcwq ? gcwq->cpu : WORK_CPU_NONE;
+       unsigned long cpu = gcwq ? gcwq->cpu : WORK_OFFQ_CPU_NONE;
 
        set_work_data(work, (cpu << WORK_OFFQ_CPU_SHIFT) | WORK_OFFQ_CANCELING,
                      WORK_STRUCT_PENDING);