61 lines
2.2 KiB
Diff
61 lines
2.2 KiB
Diff
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From 78dfb59b62d1a7735cd28fc2783e58c122954fae Mon Sep 17 00:00:00 2001
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From: Oleg Nesterov <oleg@redhat.com>
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Date: Fri, 5 Nov 2010 16:53:42 +0100
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Subject: posix-cpu-timers: workaround to suppress the problems with mt exec
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posix-cpu-timers.c correctly assumes that the dying process does
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posix_cpu_timers_exit_group() and removes all !CPUCLOCK_PERTHREAD
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timers from signal->cpu_timers list.
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But, it also assumes that timer->it.cpu.task is always the group
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leader, and thus the dead ->task means the dead thread group.
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This is obviously not true after de_thread() changes the leader.
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After that almost every posix_cpu_timer_ method has problems.
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It is not simple to fix this bug correctly. First of all, I think
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that timer->it.cpu should use struct pid instead of task_struct.
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Also, the locking should be reworked completely. In particular,
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tasklist_lock should not be used at all. This all needs a lot of
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nontrivial and hard-to-test changes.
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Change __exit_signal() to do posix_cpu_timers_exit_group() when
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the old leader dies during exec. This is not the fix, just the
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temporary hack to hide the problem for 2.6.37 and stable. IOW,
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this is obviously wrong but this is what we currently have anyway:
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cpu timers do not work after mt exec.
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In theory this change adds another race. The exiting leader can
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detach the timers which were attached to the new leader. However,
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the window between de_thread() and release_task() is small, we
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can pretend that sys_timer_create() was called before de_thread().
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Signed-off-by: Oleg Nesterov <oleg@redhat.com>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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---
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kernel/exit.c | 8 ++++++++
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1 files changed, 8 insertions(+), 0 deletions(-)
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diff --git a/kernel/exit.c b/kernel/exit.c
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index 0312022..1eff9e4 100644
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--- a/kernel/exit.c
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+++ b/kernel/exit.c
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@@ -95,6 +95,14 @@ static void __exit_signal(struct task_struct *tsk)
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sig->tty = NULL;
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} else {
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/*
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+ * This can only happen if the caller is de_thread().
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+ * FIXME: this is the temporary hack, we should teach
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+ * posix-cpu-timers to handle this case correctly.
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+ */
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+ if (unlikely(has_group_leader_pid(tsk)))
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+ posix_cpu_timers_exit_group(tsk);
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+
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+ /*
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* If there is any task waiting for the group exit
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* then notify it:
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*/
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--
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1.7.3.2
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