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authorSteven Rostedt <srostedt@redhat.com>2009-07-29 00:21:23 -0400
committerIngo Molnar <mingo@elte.hu>2009-08-02 08:26:09 -0400
commitc3a2ae3d93c0f10d29c071f599764d00b8de00cb (patch)
treee831ec79696bad3039fc9700bbb412ad38945985
parentda19ab510343c6496fe8b8f890091296032025c9 (diff)
sched: Add new prio to cpupri before removing old prio
We need to add the new prio to the cpupri accounting before removing the old prio. This is because removing the old prio first will open a race window where the cpu will be removed from pri_active. In this case the cpu will not be visible for RT push and pulls. This could cause a RT task to not migrate appropriately, and create a very large latency. This bug was found with the use of ftrace sched events and trace_printk. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <20090729042526.438281019@goodmis.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r--kernel/sched_cpupri.c30
1 files changed, 16 insertions, 14 deletions
diff --git a/kernel/sched_cpupri.c b/kernel/sched_cpupri.c
index d014efbf947a..0f052fc674d5 100644
--- a/kernel/sched_cpupri.c
+++ b/kernel/sched_cpupri.c
@@ -127,21 +127,11 @@ void cpupri_set(struct cpupri *cp, int cpu, int newpri)
127 127
128 /* 128 /*
129 * If the cpu was currently mapped to a different value, we 129 * If the cpu was currently mapped to a different value, we
130 * first need to unmap the old value 130 * need to map it to the new value then remove the old value.
131 * Note, we must add the new value first, otherwise we risk the
132 * cpu being cleared from pri_active, and this cpu could be
133 * missed for a push or pull.
131 */ 134 */
132 if (likely(oldpri != CPUPRI_INVALID)) {
133 struct cpupri_vec *vec = &cp->pri_to_cpu[oldpri];
134
135 spin_lock_irqsave(&vec->lock, flags);
136
137 vec->count--;
138 if (!vec->count)
139 clear_bit(oldpri, cp->pri_active);
140 cpumask_clear_cpu(cpu, vec->mask);
141
142 spin_unlock_irqrestore(&vec->lock, flags);
143 }
144
145 if (likely(newpri != CPUPRI_INVALID)) { 135 if (likely(newpri != CPUPRI_INVALID)) {
146 struct cpupri_vec *vec = &cp->pri_to_cpu[newpri]; 136 struct cpupri_vec *vec = &cp->pri_to_cpu[newpri];
147 137
@@ -154,6 +144,18 @@ void cpupri_set(struct cpupri *cp, int cpu, int newpri)
154 144
155 spin_unlock_irqrestore(&vec->lock, flags); 145 spin_unlock_irqrestore(&vec->lock, flags);
156 } 146 }
147 if (likely(oldpri != CPUPRI_INVALID)) {
148 struct cpupri_vec *vec = &cp->pri_to_cpu[oldpri];
149
150 spin_lock_irqsave(&vec->lock, flags);
151
152 vec->count--;
153 if (!vec->count)
154 clear_bit(oldpri, cp->pri_active);
155 cpumask_clear_cpu(cpu, vec->mask);
156
157 spin_unlock_irqrestore(&vec->lock, flags);
158 }
157 159
158 *currpri = newpri; 160 *currpri = newpri;
159} 161}