From: Davidlohr Bueso dave@stgolabs.net
commit e6a59aac8a8713f335a37d762db0dbe80e7f6d38 upstream.
do_each_pid_thread(PIDTYPE_PGID) can race with a concurrent change_pid(PIDTYPE_PGID) that can move the task from one hlist to another while iterating. Serialize ioprio_get to take the tasklist_lock in this case, just like it's set counterpart.
Fixes: d69b78ba1de (ioprio: grab rcu_read_lock in sys_ioprio_{set,get}()) Acked-by: Oleg Nesterov oleg@redhat.com Signed-off-by: Davidlohr Bueso dbueso@suse.de Link: https://lore.kernel.org/r/20211210182058.43417-1-dave@stgolabs.net Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- block/ioprio.c | 3 +++ 1 file changed, 3 insertions(+)
--- a/block/ioprio.c +++ b/block/ioprio.c @@ -202,6 +202,7 @@ SYSCALL_DEFINE2(ioprio_get, int, which, pgrp = task_pgrp(current); else pgrp = find_vpid(who); + read_lock(&tasklist_lock); do_each_pid_thread(pgrp, PIDTYPE_PGID, p) { tmpio = get_task_ioprio(p); if (tmpio < 0) @@ -211,6 +212,8 @@ SYSCALL_DEFINE2(ioprio_get, int, which, else ret = ioprio_best(ret, tmpio); } while_each_pid_thread(pgrp, PIDTYPE_PGID, p); + read_unlock(&tasklist_lock); + break; case IOPRIO_WHO_USER: uid = make_kuid(current_user_ns(), who);