Messages in this thread Patch in this message | | | From | KOSAKI Motohiro <> | Subject | Re: rcu_read_lock/unlock protect find_task_by_vpid call in migrate_pages | Date | Thu, 25 Nov 2010 18:59:58 +0900 (JST) |
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> On Thu, 2010-11-25 at 09:50 +0900, KOSAKI Motohiro wrote: > > Hi > > > > > Signed-off-by: Dave Jones <davej@redhat.com> > > > > > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > > > index 4a57f13..2f0f55b 100644 > > > --- a/mm/mempolicy.c > > > +++ b/mm/mempolicy.c > > > @@ -1308,6 +1308,7 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode, > > > > > > /* Find the mm_struct */ > > > read_lock(&tasklist_lock); > > > + rcu_read_lock(); > > > task = pid ? find_task_by_vpid(pid) : current; > > > if (!task) { > > > read_unlock(&tasklist_lock); > > > @@ -1315,6 +1316,7 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode, > > > goto out; > > > } > > > mm = get_task_mm(task); > > > + rcu_read_unlock(); > > > read_unlock(&tasklist_lock); > > > > > > err = -EINVAL; > > > > Thanks reporting. but mmotm seems already has the same patch. > > Another one,... again: > > > Do we still need the tasklist_lock in this case? > > Also, why is that think complaining, surely the tasklist_lock pins any > and all PID objects?
(cc to Christoph and Oleg)
Good spotting.
As far as I understand, find_task_by_pid() did required tasklist_lock in old days. but It isn't now.
So I think we can remove tasklist_lock from here.
=========================================================================== From 9de9f70f74e55d92b5e9057e22fc629405f63295 Mon Sep 17 00:00:00 2001 From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Date: Thu, 16 Dec 2010 17:49:23 +0900 Subject: [PATCH] mempolicy: remove tasklist_lock from migrate_pages
Today, tasklist_lock in migrate_pages doesn't protect anything. rcu_read_lock() provide enough protection from pid hash walk.
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> --- mm/mempolicy.c | 3 --- 1 files changed, 0 insertions(+), 3 deletions(-)
diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 11ff260..9064945 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -1308,16 +1308,13 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode, /* Find the mm_struct */ rcu_read_lock(); - read_lock(&tasklist_lock); task = pid ? find_task_by_vpid(pid) : current; if (!task) { - read_unlock(&tasklist_lock); rcu_read_unlock(); err = -ESRCH; goto out; } mm = get_task_mm(task); - read_unlock(&tasklist_lock); rcu_read_unlock(); err = -EINVAL; -- 1.6.5.2
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