From: ebiederm@xmission.com (Eric W. Biederman)
To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 01/23] tref: Implement task references.
Date: Sat, 04 Mar 2006 04:16:19 -0700 [thread overview]
Message-ID: <m1mzg6cvek.fsf@ebiederm.dsl.xmission.com> (raw)
In-Reply-To: <4408753B.52E3B003@tv-sign.ru> (Oleg Nesterov's message of "Fri, 03 Mar 2006 19:56:27 +0300")
Oleg Nesterov <oleg@tv-sign.ru> writes:
> Ok. I missed the virtualization/pspace discussion completely, so you are
> very probably right.
So I think the pid_ref could is likely still short several helper functions,
but is probably usable. Using it is slightly more costly but I doubt the
pid hash table has any significant performance penalties.
The important property to preserve from a maintenance standpoint is
that the helper functions take enough information that when I go back
and implement pid spaces I will need to at most tweak the pid_ref
implementation, and the pid_ref helper functions and not need to
go back through and change all of the users (again).
> Oleg.
>
> struct pid_ref
> {
> pid_t pid;
> int count;
> struct hlist_node chain;
> };
>
> // allocated in pidhash_init()
> static struct hlist_head *ref_hash;
>
> static struct pid_ref *find_pid_ref(pid_t pid)
> {
> struct hlist_node *elem;
> struct pid_ref *ref;
>
> hlist_for_each_entry(ref, elem, &ref_hash[pid_hashfn(pid)], chain)
> if (ref->pid == pid)
> return ref;
>
> return NULL;
> }
>
> // This is the only function modified.
> fastcall void free_pidmap(int pid)
> {
> pidmap_t *map = pidmap_array + pid / BITS_PER_PAGE;
> int offset = pid & BITS_PER_PAGE_MASK;
> struct pid_ref *ref;
>
> clear_bit(offset, map->page);
> atomic_inc(&map->nr_free);
>
> ref = find_pid_ref(pid);
> if (unlikely(ref != NULL)) {
> hlist_del_init(&ref->chain);
> ref->pid = 0;
> }
> }
Ouch! I believe free_pidmap now needs the tasklist_lock so
we can free the pid and kill the pid_ref atomically. Otherwise
the pid could potentially get reused before we free the pid reference.
I think that means ensuring all of the callers take tasklist_lock.
> static inline int pid_inuse(pid_t pid)
> {
> pidmap_t *map = pidmap_array + pid / BITS_PER_PAGE;
> int offset = pid & BITS_PER_PAGE_MASK;
>
> return test_bit(offset, map->page);
> }
>
> struct pid_ref *alloc_pid_ref(pid_t pid)
> {
> struct pid_ref *ref;
>
> write_lock_irq(&tasklist_lock);
> ref = find_pid_ref(pid);
> if (ref)
> ref->count++;
> else if (pid_inuse(pid)) {
> ref = kmalloc(sizeof(*ref), GFP_ATOMIC);
> if (ref) {
> ref->pid = pid;
> ref->count = 1;
> hlist_add_head(&ref->chain,
> &ref_hash[pid_hashfn(pid)]);
> }
> }
> write_unlock_irq(&tasklist_lock);
>
> return ref;
> }
I need a helper that does this from a task structure but that
is simple enough.
> void free_pid_ref(struct pid_ref *ref)
> {
> if (!ref)
> return;
>
> write_lock_irq(&tasklist_lock);
> if (!--ref->count) {
> hlist_del_init(&ref->chain);
> kfree(ref);
> }
> write_unlock_irq(&tasklist_lock);
> }
I think calling this put_pid_ref instead of free_pid_ref
is more accurate. The whole alloc/free _pid_ref instead
of the more traditional get/put kind of throws me. Since
an allocation/free is possible I can see where this comes from
but I don't feel right about those names.
Eric
next prev parent reply other threads:[~2006-03-04 11:16 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-02-23 15:52 [PATCH 00/23] proc cleanup Eric W. Biederman
2006-02-23 15:54 ` [PATCH 01/23] tref: Implement task references Eric W. Biederman
2006-02-23 15:56 ` [PATCH 02/23] proc: Fix the .. inode number on /proc/<pid>/fd Eric W. Biederman
2006-02-23 15:57 ` [PATCH 03/23] proc: Remove useless BKL in proc_pid_readlink Eric W. Biederman
2006-02-23 15:58 ` [PATCH 04/23] proc: Remove unnecessary and misleading assignments from proc_pid_make_inode Eric W. Biederman
2006-02-23 16:00 ` [PATCH 05/23] proc: Simplify the ownership rules for /proc Eric W. Biederman
2006-02-23 16:02 ` Eric W. Biederman
2006-02-23 16:04 ` [PATCH 06/23] proc: Replace proc_inode.type with proc_inode.fd Eric W. Biederman
2006-02-23 16:05 ` [PATCH 07/23] proc: Remove bogus proc_task_permission Eric W. Biederman
2006-02-23 16:06 ` [PATCH 08/23] proc: Kill proc_mem_inode_operations Eric W. Biederman
2006-02-23 16:08 ` [PATCH 09/23] proc: Properly filter out files that are not visible to a process Eric W. Biederman
2006-02-23 16:10 ` [PATCH 10/23] proc: Fix the link count for /proc/<pid>/task Eric W. Biederman
2006-02-23 16:12 ` [PATCH 11/23] proc: Move proc_maps_operations into task_mmu.c Eric W. Biederman
2006-02-23 16:15 ` [PATCH 12/23] proc: Rewrite the proc dentry flush on exit optimization Eric W. Biederman
2006-02-23 16:16 ` [PATCH 13/23] proc: Close the race of a process dying durning lookup Eric W. Biederman
2006-02-23 16:18 ` [PATCH 14/23] proc: Make PROC_NUMBUF the buffer size for holding a integers as strings Eric W. Biederman
2006-02-23 16:20 ` [PATCH 15/23] proc: refactor reading directories of tasks Eric W. Biederman
2006-02-23 16:23 ` [PATCH 16/23] proc: Don't lock task_structs indefinitely Eric W. Biederman
2006-02-23 16:24 ` [PATCH 17/23] proc: Give the root directory a task Eric W. Biederman
2006-02-23 16:25 ` [PATCH 18/23] proc: Reorder the functions in base.c Eric W. Biederman
2006-02-23 16:27 ` [PATCH 19/23] proc: Modify proc_pident_lookup to be completely table driven Eric W. Biederman
2006-02-23 16:28 ` [PATCH 20/23] proc: Make the generation of the self symlink " Eric W. Biederman
2006-02-23 16:30 ` [PATCH 21/23] proc: Factor out an instantiate method from every lookup method Eric W. Biederman
2006-02-23 16:32 ` [PATCH 22/23] proc: Remove the hard coded inode numbers Eric W. Biederman
2006-02-23 16:34 ` [PATCH 23/23] proc: Merge proc_tid_attr and proc_tgid_attr Eric W. Biederman
2006-02-23 16:49 ` [PATCH 01/23] tref: Implement task references Eric W. Biederman
2006-03-02 19:16 ` Oleg Nesterov
2006-03-02 20:37 ` Oleg Nesterov
2006-03-02 22:19 ` Eric W. Biederman
2006-03-03 16:56 ` Oleg Nesterov
2006-03-03 17:48 ` Eric W. Biederman
2006-03-04 11:16 ` Eric W. Biederman [this message]
2006-03-04 12:31 ` Oleg Nesterov
2006-03-04 17:30 ` Oleg Nesterov
2006-03-06 21:06 ` Oleg Nesterov
2006-03-06 22:18 ` Eric W. Biederman
2006-03-07 20:44 ` Oleg Nesterov
2006-03-07 1:39 ` Eric W. Biederman
2006-03-07 20:38 ` Oleg Nesterov
2006-03-07 13:12 ` Eric W. Biederman
2006-03-07 21:02 ` Oleg Nesterov
2006-03-07 23:00 ` Eric W. Biederman
2006-03-03 19:23 ` Oleg Nesterov
2006-03-04 10:51 ` Eric W. Biederman
2006-02-25 12:27 ` [PATCH 00/23] proc cleanup Andrew Morton
2006-02-25 13:34 ` Eric W. Biederman
2006-02-25 15:20 ` Eric W. Biederman
2006-02-27 15:26 ` Serge E. Hallyn
2006-02-27 15:56 ` Eric W. Biederman
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