The move_pages() usage of find_task_by_vpid() requires rcu_read_lock()
to prevent free_pid() from reclaiming the pid.
Without this patch, RCU warnings are printed in v2.6.38-rc4 move_pages()
with:
CONFIG_LOCKUP_DETECTOR=y
CONFIG_PREEMPT=y
CONFIG_LOCKDEP=y
CONFIG_PROVE_LOCKING=y
CONFIG_PROVE_RCU=y
Previously, migrate_pages() went through a similar transformation
replacing usage of tasklist_lock with rcu read lock:
commit 55cfaa3cbdd29c4919ecb5fb8965c310f357e48c
Author: Zeng Zhaoming <zengzm.kernel@xxxxxxxxx>
Date: Thu Dec 2 14:31:13 2010 -0800
mm/mempolicy.c: add rcu read lock to protect pid structure
commit 1e50df39f6e2c3a4a3394df62baa8a213df16c54
Author: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Date: Thu Jan 13 15:46:14 2011 -0800
mempolicy: remove tasklist_lock from migrate_pages
Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx>
---
mm/migrate.c | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/migrate.c b/mm/migrate.c
index 7661152..352de555 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1287,14 +1287,14 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
return -EPERM;
/* 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);
+ rcu_read_unlock();
return -ESRCH;
}
mm = get_task_mm(task);
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
if (!mm)
return -EINVAL;
--
1.7.3.1
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