Messages in this thread Patch in this message | | | Date | Sun, 1 Apr 2012 23:38:04 +0200 | From | Oleg Nesterov <> | Subject | [PATCH 1/2] tracing: syscall_*regfunc() can race with copy_process() |
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syscall_regfunc() and syscall_unregfunc() should set/clear TIF_SYSCALL_TRACEPOINT system-wide, but do_each_thread() can race with copy_process() and miss the new child which was not added to init_task.tasks list yet.
Change copy_process() to update the child's TIF_SYSCALL_TRACEPOINT under tasklist.
While at it,
- remove _irqsafe from syscall_regfunc/syscall_unregfunc, read_lock(tasklist) doesn't need to disable irqs.
- change syscall_unregfunc() to check PF_KTHREAD to skip the kernel threads, ->mm != NULL is the common mistake.
Note: probably this check should be simply removed, needs another patch.
Signed-off-by: Oleg Nesterov <oleg@redhat.com> --- kernel/fork.c | 7 +++++++ kernel/tracepoint.c | 12 +++++------- 2 files changed, 12 insertions(+), 7 deletions(-)
diff --git a/kernel/fork.c b/kernel/fork.c index 34d7ed1..772d4a5 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1446,7 +1446,14 @@ static struct task_struct *copy_process(unsigned long clone_flags, total_forks++; spin_unlock(¤t->sighand->siglock); +#ifdef CONFIG_TRACEPOINTS + if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) + set_tsk_thread_flag(p, TIF_SYSCALL_TRACEPOINT); + else + clear_tsk_thread_flag(p, TIF_SYSCALL_TRACEPOINT); +#endif write_unlock_irq(&tasklist_lock); + proc_fork_connector(p); cgroup_post_fork(p); if (clone_flags & CLONE_THREAD) diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c index f1539de..e2a4523 100644 --- a/kernel/tracepoint.c +++ b/kernel/tracepoint.c @@ -734,33 +734,31 @@ static int sys_tracepoint_refcount; void syscall_regfunc(void) { - unsigned long flags; struct task_struct *g, *t; if (!sys_tracepoint_refcount) { - read_lock_irqsave(&tasklist_lock, flags); + read_lock(&tasklist_lock); do_each_thread(g, t) { /* Skip kernel threads. */ - if (t->mm) + if (!(t->flags & PF_KTHREAD)) set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT); } while_each_thread(g, t); - read_unlock_irqrestore(&tasklist_lock, flags); + read_unlock(&tasklist_lock); } sys_tracepoint_refcount++; } void syscall_unregfunc(void) { - unsigned long flags; struct task_struct *g, *t; sys_tracepoint_refcount--; if (!sys_tracepoint_refcount) { - read_lock_irqsave(&tasklist_lock, flags); + read_lock(&tasklist_lock); do_each_thread(g, t) { clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT); } while_each_thread(g, t); - read_unlock_irqrestore(&tasklist_lock, flags); + read_unlock(&tasklist_lock); } } #endif -- 1.5.5.1
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