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BUG/MINOR: task: close a tiny race in the inter-thread wakeup

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__task_wakeup() takes care of a small race that exists between threads,
but it uses a store barrier that is not sufficient since apparently the
state read after clearing the leaf_p pointer sometimes is incorrect. This
results in missed wakeups between threads competing at a high rate. Let's
use a full barrier instead to serialize the operations.

This may be backported to 1.9 though it's extremely unlikely that this
bug will ever manifest itself there.
This commit is contained in:
Willy Tarreau 2019-02-04 10:26:53 +01:00
parent ef6fd85623
commit 155acffc13
1 changed files with 1 additions and 1 deletions
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2
src/task.c
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@ -107,7 +107,7 @@ redo:
if (((volatile unsigned short)(t->state)) & TASK_RUNNING) { if (((volatile unsigned short)(t->state)) & TASK_RUNNING) {
unsigned short state; unsigned short state;
t->rq.node.leaf_p = NULL; t->rq.node.leaf_p = NULL;
__ha_barrier_store(); __ha_barrier_full();
state = (volatile unsigned short)(t->state); state = (volatile unsigned short)(t->state);
if (unlikely(state != 0 && !(state & TASK_RUNNING))) if (unlikely(state != 0 && !(state & TASK_RUNNING)))