From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id CBACE6B00B6 for ; Fri, 12 Nov 2010 02:33:02 -0500 (EST) From: Greg Thelen Subject: [PATCH] ioprio: grab rcu_read_lock in sys_ioprio_{set,get}() Date: Thu, 11 Nov 2010 23:32:47 -0800 Message-Id: <1289547167-32675-1-git-send-email-gthelen@google.com> Sender: owner-linux-mm@kvack.org To: Andrew Morton , Oleg Nesterov , Jens Axboe , "Paul E. McKenney" Cc: Greg Thelen , Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: 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: [] sys_ioprio_set+0x7f/0x29e stack backtrace: Pid: 1355, comm: ureadahead Not tainted 2.6.37-dbg-DEV #1 Call Trace: [] lockdep_rcu_dereference+0xaa/0xb3 [] find_task_by_pid_ns+0x44/0x5d [] find_task_by_vpid+0x22/0x24 [] sys_ioprio_set+0xb4/0x29e [] ? trace_hardirqs_off_thunk+0x3a/0x3c [] sysenter_dispatch+0x7/0x2c [] ? 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 --- fs/ioprio.c | 13 ++++--------- 1 files changed, 4 insertions(+), 9 deletions(-) diff --git a/fs/ioprio.c b/fs/ioprio.c index 748cfb9..7da2a06 100644 --- a/fs/ioprio.c +++ b/fs/ioprio.c @@ -103,12 +103,7 @@ 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: if (!who) @@ -153,7 +148,7 @@ free_uid: ret = -EINVAL; } - read_unlock(&tasklist_lock); + rcu_read_unlock(); return ret; } @@ -197,7 +192,7 @@ 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: if (!who) @@ -250,6 +245,6 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who) ret = -EINVAL; } - read_unlock(&tasklist_lock); + rcu_read_unlock(); return ret; } -- 1.7.3.1 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org