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Date: Wed, 19 Dec 2012 04:13:30 -0800
From: "Eric W. Biederman" <ebiederm@...ssion.com>
To: Xiaotian Feng <xtfeng@...il.com>, akpm@...ux-foundation.org
CC: Xiaotian Feng <dannyfeng@...cent.com>,
Al Viro <viro@...iv.linux.org.uk>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] proc: fix inconsistent lock state
Xiaotian Feng <xtfeng@...il.com> wrote:
>Lockdep found an inconsistent lock state when rcu is processing
>delayed work in softirq. Currently, kernel is using
>spin_lock/spin_unlock
>to protect proc_inum_ida, but proc_free_inum is called by rcu in
>softirq
>context.
Emarassing. Thank you for finding this.
Something doesn't feel right. I don't think there should be a path where we get to proc_free_inum from bh context.
Rcu callbacks should be running in process context (if a special one).
I need to sleep on this one but do_softirq -> rcu_process_callbacks seems wrong.
I will dig into this more after I have finished sleeping. What rcu options do you have selected?
Eric
>Use spin_lock_bh/spin_unlock_bh fix following lockdep warning.
>
>[ 49.709127] =================================
>[ 49.709360] [ INFO: inconsistent lock state ]
>[ 49.709593] 3.7.0 #36 Not tainted
>[ 49.709846] ---------------------------------
>[ 49.710080] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
>[ 49.710377] swapper/1/0 [HC0[0]:SC1[1]:HE1:SE0] takes:
>[ 49.710640] (proc_inum_lock){+.?...}, at: [<ffffffff8124280c>]
>proc_free_inum+0x1c/0x50
>[ 49.711287] {SOFTIRQ-ON-W} state was registered at:
>[ 49.711540] [<ffffffff8110dc4e>] __lock_acquire+0x8ae/0xca0
>[ 49.711896] [<ffffffff8110e1d9>] lock_acquire+0x199/0x200
>[ 49.712242] [<ffffffff81b295e1>] _raw_spin_lock+0x41/0x50
>[ 49.712590] [<ffffffff81242efc>] proc_alloc_inum+0x4c/0xd0
>[ 49.712941] [<ffffffff811f1799>] alloc_mnt_ns+0x49/0xc0
>[ 49.713282] [<ffffffff811f3365>] create_mnt_ns+0x25/0x70
>[ 49.713625] [<ffffffff82115443>] mnt_init+0x161/0x1c7
>[ 49.713962] [<ffffffff82114f51>] vfs_caches_init+0x107/0x11a
>[ 49.714392] [<ffffffff820f3c67>] start_kernel+0x348/0x38c
>[ 49.714815] [<ffffffff820f3335>]
>x86_64_start_reservations+0x131/0x136
>[ 49.715279] [<ffffffff820f343d>] x86_64_start_kernel+0x103/0x112
>[ 49.715728] irq event stamp: 2993422
>[ 49.716006] hardirqs last enabled at (2993422):
>[<ffffffff81b29f75>] _raw_spin_unlock_irqrestore+0x55/0x80
>[ 49.716661] hardirqs last disabled at (2993421):
>[<ffffffff81b296f9>] _raw_spin_lock_irqsave+0x29/0x70
>[ 49.717300] softirqs last enabled at (2993394):
>[<ffffffff810ab0b3>] _local_bh_enable+0x13/0x20
>[ 49.717920] softirqs last disabled at (2993395):
>[<ffffffff81b2c33c>] call_softirq+0x1c/0x30
>[ 49.718528]
>[ 49.718528] other info that might help us debug this:
>[ 49.718992] Possible unsafe locking scenario:
>[ 49.718992]
>[ 49.719433] CPU0
>[ 49.719669] ----
>[ 49.719902] lock(proc_inum_lock);
>[ 49.720308] <Interrupt>
>[ 49.720548] lock(proc_inum_lock);
>[ 49.720961]
>[ 49.720961] *** DEADLOCK ***
>[ 49.720961]
>[ 49.721477] no locks held by swapper/1/0.
>[ 49.721769]
>[ 49.721769] stack backtrace:
>[ 49.722150] Pid: 0, comm: swapper/1 Not tainted 3.7.0 #36
>[ 49.722555] Call Trace:
>[ 49.722787] <IRQ> [<ffffffff810a40f1>] ? vprintk_emit+0x471/0x510
>[ 49.723307] [<ffffffff81109ce5>] print_usage_bug+0x2a5/0x2c0
>[ 49.723671] [<ffffffff8110a03b>] mark_lock+0x33b/0x5e0
>[ 49.724014] [<ffffffff8110dbb3>] __lock_acquire+0x813/0xca0
>[ 49.724374] [<ffffffff8110a8ad>] ? trace_hardirqs_on+0xd/0x10
>[ 49.724741] [<ffffffff8110e1d9>] lock_acquire+0x199/0x200
>[ 49.725095] [<ffffffff8124280c>] ? proc_free_inum+0x1c/0x50
>[ 49.725455] [<ffffffff81b295e1>] _raw_spin_lock+0x41/0x50
>[ 49.725806] [<ffffffff8124280c>] ? proc_free_inum+0x1c/0x50
>[ 49.726165] [<ffffffff8124280c>] proc_free_inum+0x1c/0x50
>[ 49.726519] [<ffffffff810c76a2>] ? put_pid+0x42/0x60
>[ 49.726857] [<ffffffff81128cac>] free_pid_ns+0x1c/0x50
>[ 49.727201] [<ffffffff81128d0e>] put_pid_ns+0x2e/0x50
>[ 49.727540] [<ffffffff810c76aa>] put_pid+0x4a/0x60
>[ 49.727868] [<ffffffff810c76d2>] delayed_put_pid+0x12/0x20
>[ 49.728225] [<ffffffff81132ed2>] rcu_process_callbacks+0x462/0x790
>[ 49.728606] [<ffffffff810ab4e4>] __do_softirq+0x1b4/0x3b0
>[ 49.728959] [<ffffffff81104132>] ?
>clockevents_program_event+0xc2/0xf0
>[ 49.729354] [<ffffffff81b2c33c>] call_softirq+0x1c/0x30
>[ 49.729702] [<ffffffff81057bf9>] do_softirq+0x59/0xd0
>[ 49.730039] [<ffffffff810ab024>] irq_exit+0x54/0xd0
>[ 49.730370] [<ffffffff81b2ca05>] smp_apic_timer_interrupt+0x95/0xa3
>[ 49.730755] [<ffffffff81b2bbf2>] apic_timer_interrupt+0x72/0x80
>[ 49.731124] <EOI> [<ffffffff81b2a473>] ?
>retint_restore_args+0x13/0x13
>[ 49.731658] [<ffffffff8199d125>] ? cpuidle_wrap_enter+0x55/0xa0
>[ 49.732029] [<ffffffff8199d121>] ? cpuidle_wrap_enter+0x51/0xa0
>[ 49.732399] [<ffffffff8199d180>] cpuidle_enter_tk+0x10/0x20
>[ 49.732759] [<ffffffff8199cb57>] cpuidle_enter_state+0x17/0x50
>[ 49.733128] [<ffffffff8199d507>] cpuidle_idle_call+0x287/0x520
>[ 49.733496] [<ffffffff8105feca>] cpu_idle+0xba/0x130
>[ 49.733830] [<ffffffff81b2059f>] start_secondary+0x2b3/0x2bc
>
>Signed-off-by: Xiaotian Feng <dannyfeng@...cent.com>
>Cc: Andrew Morton <akpm@...ux-foundation.org>
>Cc: Al Viro <viro@...iv.linux.org.uk>
>Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
>Cc: linux-kernel@...r.kernel.org
>---
> fs/proc/generic.c | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
>diff --git a/fs/proc/generic.c b/fs/proc/generic.c
>index 7b3ae3c..e659a0f 100644
>--- a/fs/proc/generic.c
>+++ b/fs/proc/generic.c
>@@ -359,18 +359,18 @@ retry:
> if (!ida_pre_get(&proc_inum_ida, GFP_KERNEL))
> return -ENOMEM;
>
>- spin_lock(&proc_inum_lock);
>+ spin_lock_bh(&proc_inum_lock);
> error = ida_get_new(&proc_inum_ida, &i);
>- spin_unlock(&proc_inum_lock);
>+ spin_unlock_bh(&proc_inum_lock);
> if (error == -EAGAIN)
> goto retry;
> else if (error)
> return error;
>
> if (i > UINT_MAX - PROC_DYNAMIC_FIRST) {
>- spin_lock(&proc_inum_lock);
>+ spin_lock_bh(&proc_inum_lock);
> ida_remove(&proc_inum_ida, i);
>- spin_unlock(&proc_inum_lock);
>+ spin_unlock_bh(&proc_inum_lock);
> return -ENOSPC;
> }
> *inum = PROC_DYNAMIC_FIRST + i;
>@@ -379,9 +379,9 @@ retry:
>
> void proc_free_inum(unsigned int inum)
> {
>- spin_lock(&proc_inum_lock);
>+ spin_lock_bh(&proc_inum_lock);
> ida_remove(&proc_inum_ida, inum - PROC_DYNAMIC_FIRST);
>- spin_unlock(&proc_inum_lock);
>+ spin_unlock_bh(&proc_inum_lock);
> }
>
>static void *proc_follow_link(struct dentry *dentry, struct nameidata
>*nd)
--
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