ioprio: grab rcu_read_lock in sys_ioprio_{set,get}() (d69b78ba) · Commits · 戴 / test

Using: - CONFIG_LOCKUP_DETECTOR=y - CONFIG_PREEMPT=y - CONFIG_LOCKDEP=y - CONFIG_PROVE_LOCKING=y - CONFIG_PROVE_RCU=y found a missing rcu lock during boot on a 512 MiB x86_64 ubuntu vm: =================================================== [ INFO: suspicious rcu_dereference_check() usage. ] --------------------------------------------------- kernel/pid.c:419 invoked rcu_dereference_check() without protection! other info that might help us debug this: rcu_scheduler_active = 1, debug_locks = 0 1 lock held by ureadahead/1355: #0: (tasklist_lock){.+.+..}, at: [<ffffffff8115bc09>] sys_ioprio_set+0x7f/0x29e stack backtrace: Pid: 1355, comm: ureadahead Not tainted 2.6.37-dbg-DEV #1 Call Trace: [<ffffffff8109c10c>] lockdep_rcu_dereference+0xaa/0xb3 [<ffffffff81088cbf>] find_task_by_pid_ns+0x44/0x5d [<ffffffff81088cfa>] find_task_by_vpid+0x22/0x24 [<ffffffff8115bc3e>] sys_ioprio_set+0xb4/0x29e [<ffffffff8147cf21>] ? trace_hardirqs_off_thunk+0x3a/0x3c [<ffffffff8105c409>] sysenter_dispatch+0x7/0x2c [<ffffffff8147cee2>] ? trace_hardirqs_on_thunk+0x3a/0x3f The fix is to: a) grab rcu lock in sys_ioprio_{set,get}() and b) avoid grabbing tasklist_lock. Discussion in: http://marc.info/?l=linux-kernel&m=128951324702889 Signed-off-by:

Greg Thelen <gthelen@google.com> Acked-by:

Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by:

Oleg Nesterov <oleg@redhat.com> Modified by Jens to remove the now redundant inner rcu lock and unlock since they are now protected by the outer lock. Signed-off-by:

Jens Axboe <jaxboe@fusionio.com>

fs/ioprio.c

+6 −25

Original line number	Diff line number	Diff line
		@@ -103,22 +103,15 @@ SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
		}

		ret = -ESRCH;
		/*
		* We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
		* so we can't use rcu_read_lock(). See re-copy of ->ioprio
		* in copy_process().
		*/
		read_lock(&tasklist_lock);
		rcu_read_lock();
		switch (which) {
		case IOPRIO_WHO_PROCESS:
		rcu_read_lock();
		if (!who)
		p = current;
		else
		p = find_task_by_vpid(who);
		if (p)
		ret = set_task_ioprio(p, ioprio);
		rcu_read_unlock();
		break;
		case IOPRIO_WHO_PGRP:
		if (!who)
		@@ -141,12 +134,7 @@ SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
		break;

		do_each_thread(g, p) {
		int match;

		rcu_read_lock();
		match = __task_cred(p)->uid == who;
		rcu_read_unlock();
		if (!match)
		if (__task_cred(p)->uid != who)
		continue;
		ret = set_task_ioprio(p, ioprio);
		if (ret)
		@@ -160,7 +148,7 @@ free_uid:
		ret = -EINVAL;
		}

		read_unlock(&tasklist_lock);
		rcu_read_unlock();
		return ret;
		}

		@@ -204,17 +192,15 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
		int ret = -ESRCH;
		int tmpio;

		read_lock(&tasklist_lock);
		rcu_read_lock();
		switch (which) {
		case IOPRIO_WHO_PROCESS:
		rcu_read_lock();
		if (!who)
		p = current;
		else
		p = find_task_by_vpid(who);
		if (p)
		ret = get_task_ioprio(p);
		rcu_read_unlock();
		break;
		case IOPRIO_WHO_PGRP:
		if (!who)
		@@ -241,12 +227,7 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
		break;

		do_each_thread(g, p) {
		int match;

		rcu_read_lock();
		match = __task_cred(p)->uid == user->uid;
		rcu_read_unlock();
		if (!match)
		if (__task_cred(p)->uid != user->uid)
		continue;
		tmpio = get_task_ioprio(p);
		if (tmpio < 0)
		@@ -264,6 +245,6 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
		ret = -EINVAL;
		}

		read_unlock(&tasklist_lock);
		rcu_read_unlock();
		return ret;
		}

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