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Message-Id: <1840e47fc4113af16989a4250d98bed62a9bce53.1354559528.git.luto@amacapital.net>
Date: Mon, 3 Dec 2012 10:32:28 -0800
From: Andy Lutomirski <luto@...capital.net>
To: linux-kernel@...r.kernel.org
Cc: Andy Lutomirski <luto@...capital.net>
Subject: [PATCH] Make task directories in /proc pollable
This has been a requested feature for a long time [1][2].
/proc/<pid> and /proc/<tgid>/task/<pid> will show POLLIN | POLLRDNORM
when the <pid> is dead and POLLIN | POLLRDNORM | POLLERR when <pid> is
dead and reaped.
The ability to tell whether the task exists given an fd isn't new -- readdir
can do it. The ability to distinguish live and zombie tasks by fd may
have minor security implications.
It's conceivable, although unlikely, that some existing software expects
directories in /proc to always have POLLIN set. The benefit of using POLLIN
instead of something like POLLPRI is feature detection -- checking /proc/self
for POLLIN will reliably detect this feature.
[1] http://lwn.net/Articles/462177/
[2] http://0pointer.de/blog/projects/plumbers-wishlist-3.html
Signed-off-by: Andy Lutomirski <luto@...capital.net>
---
fs/proc/base.c | 26 ++++++++++++++++++++++++++
include/linux/init_task.h | 2 ++
include/linux/sched.h | 3 +++
kernel/exit.c | 3 +++
kernel/fork.c | 4 ++++
5 files changed, 38 insertions(+)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 3c231ad..ebab7ec 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2737,9 +2737,34 @@ static int proc_tgid_base_readdir(struct file * filp,
tgid_base_stuff,ARRAY_SIZE(tgid_base_stuff));
}
+static unsigned int proc_task_base_poll(struct file *filp,
+ struct poll_table_struct *wait)
+{
+ struct task_struct *task;
+ int retval;
+
+ task = get_proc_task(filp->f_path.dentry->d_inode);
+ if (!task)
+ return POLLIN | POLLRDNORM | POLLERR;
+
+ read_lock(&tasklist_lock);
+ poll_wait(filp, &task->detach_wqh, wait);
+ if (task_is_dead(task)) {
+ retval = POLLIN | POLLRDNORM;
+ } else {
+ retval = 0;
+ poll_wait(filp, &task->exit_wqh, wait);
+ }
+ read_unlock(&tasklist_lock);
+
+ put_task_struct(task);
+ return retval;
+}
+
static const struct file_operations proc_tgid_base_operations = {
.read = generic_read_dir,
.readdir = proc_tgid_base_readdir,
+ .poll = proc_task_base_poll,
.llseek = default_llseek,
};
@@ -3110,6 +3135,7 @@ static struct dentry *proc_tid_base_lookup(struct inode *dir, struct dentry *den
static const struct file_operations proc_tid_base_operations = {
.read = generic_read_dir,
.readdir = proc_tid_base_readdir,
+ .poll = proc_task_base_poll,
.llseek = default_llseek,
};
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 6d087c5..093379e 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -202,6 +202,8 @@ extern struct task_group root_task_group;
[PIDTYPE_SID] = INIT_PID_LINK(PIDTYPE_SID), \
}, \
.thread_group = LIST_HEAD_INIT(tsk.thread_group), \
+ .exit_wqh = __WAIT_QUEUE_HEAD_INITIALIZER(tsk.exit_wqh), \
+ .detach_wqh = __WAIT_QUEUE_HEAD_INITIALIZER(tsk.detach_wqh),\
INIT_IDS \
INIT_PERF_EVENTS(tsk) \
INIT_TRACE_IRQFLAGS \
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 0dd42a0..6034a37 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1548,6 +1548,9 @@ struct task_struct {
#ifdef CONFIG_UPROBES
struct uprobe_task *utask;
#endif
+
+ /* These are woken with tasklist_lock held. */
+ wait_queue_head_t exit_wqh, detach_wqh;
};
/* Future-safe accessor for struct task_struct's cpus_allowed. */
diff --git a/kernel/exit.c b/kernel/exit.c
index 346616c..01c584b 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -212,6 +212,7 @@ repeat:
leader->exit_state = EXIT_DEAD;
}
+ wake_up_all(&p->detach_wqh);
write_unlock_irq(&tasklist_lock);
release_thread(p);
call_rcu(&p->rcu, delayed_put_task_struct);
@@ -775,6 +776,8 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
/* mt-exec, de_thread() is waiting for group leader */
if (unlikely(tsk->signal->notify_count < 0))
wake_up_process(tsk->signal->group_exit_task);
+
+ wake_up_all(&tsk->exit_wqh);
write_unlock_irq(&tasklist_lock);
/* If the process is dead, release it - nobody will wait for it */
diff --git a/kernel/fork.c b/kernel/fork.c
index 8b20ab7..356b32c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -235,6 +235,8 @@ void __put_task_struct(struct task_struct *tsk)
WARN_ON(!tsk->exit_state);
WARN_ON(atomic_read(&tsk->usage));
WARN_ON(tsk == current);
+ WARN_ON(waitqueue_active(&tsk->exit_wqh));
+ WARN_ON(waitqueue_active(&tsk->detach_wqh));
security_task_free(tsk);
exit_creds(tsk);
@@ -1285,6 +1287,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
p->memcg_batch.do_batch = 0;
p->memcg_batch.memcg = NULL;
#endif
+ init_waitqueue_head(&p->exit_wqh);
+ init_waitqueue_head(&p->detach_wqh);
/* Perform scheduler related setup. Assign this task to a CPU. */
sched_fork(p);
--
1.7.11.7
--
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