lkml.org 
[lkml]   [2013]   [May]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 3/3] proc: simplify proc_task_readdir/first_tid paths
On 05/28, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@redhat.com> writes:
>
> > proc_task_readdir() does not really need "leader", first_tid()
> > has to revalidate it anyway. Just pass proc_pid(inode) to
> > first_tid() instead, it can do pid_task(PIDTYPE_PID) itself
> > and read ->group_leader only if necessary.
> >
> > Note: I am not sure proc_task_readdir() really needs the initial
> > -ENOENT check, but this is what the current code does.
>
> This looks like a nice cleanup.
>
> We would need either -ENOENT or a return of 0 and an empty directory at
> the least. We need the check so that empty directories don't have "."
> and ".." entries.

And this is not clear to me...

Why the empty "." + ".." dir is bad if the task(s) has gone away after
opendir?

> > if (tid && (nr > 0)) {
> > pos = find_task_by_pid_ns(tid, ns);
> > - if (pos && (pos->group_leader == leader))
> > + if (pos && same_thread_group(pos, task))
>
> Sigh this reminds me we need to figure out how to kill task->pid and
> task->tgid,

Yeah.

> which I assume means fixing same_thread_group.

Now that ->signal can't go away before task_struct, we can make it

static inline
int same_thread_group(struct task_struct *p1, struct task_struct *p2)
{
return p1->signal == p2->signal;
}


> > + if (!pid_task(proc_pid(inode), PIDTYPE_PID))
> > + return -ENOENT;
>
> Strictly speaking this call to pid_task needs to be in a rcu critical
> section.

Argh, thanks.

we do not really need rcu, we are not going to dereference this pointer,
but we should make __rcu_dereference_check() happy...

I'll change this... but once again, can't we simply remove this check?






While you are here. Could you explain the ->d_inode check in
proc_fill_cache() ? The code _looks_ wrong,

if (!child || IS_ERR(child) || !child->d_inode)
goto end_instantiate;

If d_inode == NULL, who does dput() ?

OTOH, if we ensure d_inode != NULL, why do we check "if (inode)" after
inode = child->d_inode ?

IOW, it seems that this check should be simply removed?

Oleg.



\
 
 \ /
  Last update: 2013-05-29 20:01    [W:0.064 / U:0.060 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site