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Message-ID: <YG7Q5C4Rb5dx5GFx@hirez.programming.kicks-ass.net>
Date: Thu, 8 Apr 2021 11:46:12 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Jens Axboe <axboe@...nel.dk>, Oleg Nesterov <oleg@...hat.com>
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] block: Fix sys_ioprio_set(.which=IOPRIO_WHO_PGRP) task
iteration
do_each_pid_thread() { } while_each_pid_thread() is a double loop and
thus break doesn't work as expected. Also, it should be used under
tasklist_lock because otherwise we can race against change_pid() for
PGID/SID.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
block/ioprio.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
--- a/block/ioprio.c
+++ b/block/ioprio.c
@@ -119,11 +119,17 @@ SYSCALL_DEFINE3(ioprio_set, int, which,
pgrp = task_pgrp(current);
else
pgrp = find_vpid(who);
+
+ read_lock(&tasklist_lock);
do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
ret = set_task_ioprio(p, ioprio);
- if (ret)
- break;
+ if (ret) {
+ read_unlock(&tasklist_lock);
+ goto out;
+ }
} while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
+ read_unlock(&tasklist_lock);
+
break;
case IOPRIO_WHO_USER:
uid = make_kuid(current_user_ns(), who);
@@ -153,6 +159,7 @@ SYSCALL_DEFINE3(ioprio_set, int, which,
ret = -EINVAL;
}
+out:
rcu_read_unlock();
return ret;
}
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