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BUG/MAJOR: task: make sure never to delete a queued task 

Commit 0c7a4b6 ("MINOR: tasks: Don't set the TASK_RUNNING flag when
adding in the tasklet list.") revealed a hole in the way tasks may
be freed : they could be removed while in the run queue when the
TASK_QUEUED flag was present but not the TASK_RUNNING one. But it
seems the issue was emphasized by commit cde7902 ("MEDIUM: tasks:
improve fairness between the local and global queues") though the
code it replaces was already affected given how late the TASK_RUNNING
flag was set after removal from the global queue.

At the moment the task is picked from the global run queue, if it
is the last one, the global run queue lock is dropped, and then
the TASK_RUNNING flag was added. In the mean time another thread
might have performed a task_free(), and immediately after, the
TASK_RUNNING flag was re-added to the task, which was then added
to the tasklet list. The unprotected window was extremely faint
but does definitely exist and inconsistent task lists have been
observed a few times during very intensive tests over the last few
days. From this point various options are possible, the task might
have been re-allocated while running, and assigned state 0 and/or
state QUEUED while it was still running, resulting in the tast not
being put back into the tree.

This commit simply makes sure that tests on TASK_RUNNING before removing
the task also cover TASK_QUEUED.

It must be backported to 1.9 along with the previous ones touching
that area.
This commit is contained in:
Willy Tarreau 2019-04-17 21:58:23 +02:00
parent 51205a1958
commit a70bfaaf8b
2 changed files with 2 additions and 2 deletions
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2
include/proto/applet.h
View File

@ -103,7 +103,7 @@ static inline void appctx_free(struct appctx *appctx)
/* The task is supposed to be run on this thread, so we can just
* check if it's running already (or about to run) or not
*/
if (!(appctx->t->state & TASK_RUNNING))
if (!(appctx->t->state & (TASK_QUEUED | TASK_RUNNING)))
__appctx_free(appctx);
else {
/* if it's running, or about to run, defer the freeing

2
include/proto/task.h
View File

@ -355,7 +355,7 @@ static inline void task_free(struct task *t)
/* There's no need to protect t->state with a lock, as the task
* has to run on the current thread.
*/
if (t == curr_task || !(t->state & TASK_RUNNING))
if (t == curr_task || !(t->state & (TASK_QUEUED | TASK_RUNNING)))
__task_free(t);
else
t->process = NULL;