Low WORK_STRUCT_FLAG_BITS bits of work_struct->data contain
WORK_STRUCT_FLAG_* and flush color. If the work item is queued, the
rest point to the cpu_workqueue with WORK_STRUCT_CWQ set; otherwise,
WORK_STRUCT_CWQ is clear and the bits contain the last CPU number -
either a real CPU number or one of WORK_CPU_*.
Scheduled addition of mod_delayed_work[_on]() requires an additional
flag, which is used only while a work item is off queue. There are
more than enough bits to represent off-queue CPU number on both 32 and
64bits. This patch introduces WORK_OFFQ_FLAG_* which occupy the lower
part of the @work->data high bits while off queue. This patch doesn't
define any actual OFFQ flag yet.
Off-queue CPU number is now shifted by WORK_OFFQ_CPU_SHIFT, which adds
the number of bits used by OFFQ flags to WORK_STRUCT_FLAG_SHIFT, to
make room for OFFQ flags.
To avoid shift width warning with large WORK_OFFQ_FLAG_BITS, ulong
cast is added to WORK_STRUCT_NO_CPU and, just in case, BUILD_BUG_ON()
to check that there are enough bits to accomodate off-queue CPU number
is added.
This patch doesn't make any functional difference.
Signed-off-by: Tejun Heo <t...@kernel.org>
---
include/linux/workqueue.h | 8 +++++++-
kernel/workqueue.c | 14 +++++++++-----
2 files changed, 16 insertions(+), 6 deletions(-)
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index ab95fef..f562674 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -68,9 +68,15 @@ enum {
WORK_STRUCT_FLAG_BITS = WORK_STRUCT_COLOR_SHIFT +
WORK_STRUCT_COLOR_BITS,
+ /* data contains off-queue information when !WORK_STRUCT_CWQ */
+ WORK_OFFQ_FLAG_BASE = WORK_STRUCT_FLAG_BITS,
+ WORK_OFFQ_FLAG_BITS = 0,
+ WORK_OFFQ_CPU_SHIFT = WORK_OFFQ_FLAG_BASE + WORK_OFFQ_FLAG_BITS,
+
+ /* 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 = WORK_CPU_NONE << WORK_STRUCT_FLAG_BITS,
+ WORK_STRUCT_NO_CPU = (unsigned long)WORK_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 0f50f40..eeae770 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -533,9 +533,9 @@ static int work_next_color(int color)
}
/*
- * A work's data points to the cwq with WORK_STRUCT_CWQ set while the
- * work is on queue. Once execution starts, WORK_STRUCT_CWQ is
- * cleared and the work data contains the cpu number it was last on.
+ * While queued, %WORK_STRUCT_CWQ is set and non flag bits of a work's data
+ * contain the pointer to the queued cwq. Once execution starts, the flag
+ * is cleared and the high bits contain OFFQ flags and CPU number.
*
* set_work_cwq(), set_work_cpu_and_clear_pending() and clear_work_data()
* can be used to set the cwq, cpu or clear work->data. These functions
@@ -565,7 +565,7 @@ static void set_work_cwq(struct work_struct *work,
static void set_work_cpu_and_clear_pending(struct work_struct *work,
unsigned int cpu)
{
- set_work_data(work, cpu << WORK_STRUCT_FLAG_BITS, 0);
+ set_work_data(work, (unsigned long)cpu << WORK_OFFQ_CPU_SHIFT, 0);
}
static void clear_work_data(struct work_struct *work)
@@ -592,7 +592,7 @@ static struct global_cwq *get_work_gcwq(struct work_struct
*work)
return ((struct cpu_workqueue_struct *)
(data & WORK_STRUCT_WQ_DATA_MASK))->pool->gcwq;
- cpu = data >> WORK_STRUCT_FLAG_BITS;
+ cpu = data >> WORK_OFFQ_CPU_SHIFT;
if (cpu == WORK_CPU_NONE)
return NULL;
@@ -3724,6 +3724,10 @@ static int __init init_workqueues(void)
unsigned int cpu;
int i;
+ /* make sure we have enough bits for OFFQ CPU number */
+ BUILD_BUG_ON((1LU << (BITS_PER_LONG - WORK_OFFQ_CPU_SHIFT)) <
+ WORK_CPU_LAST);
+
cpu_notifier(workqueue_cpu_up_callback, CPU_PRI_WORKQUEUE_UP);
cpu_notifier(workqueue_cpu_down_callback, CPU_PRI_WORKQUEUE_DOWN);
--
1.7.7.3
--
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