tree 15fb43322af3ec59da85e22e052e31384f2d4aee
parent 51205a1958f5e83121deac1d4e818bd5712fe12d
author Willy Tarreau <w@1wt.eu> 1555531103 +0200
committer Willy Tarreau <w@1wt.eu> 1555532158 +0200
encoding latin1

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.