Re: rcu: fix hlist_bl_set_first_rcu annotation
From: Andrew Price
Date: Thu Feb 14 2013 - 19:01:47 EST
Hi,
On 03/02/13 18:39, Paul E. McKenney wrote:
On Wed, Jan 30, 2013 at 07:07:57PM +0000, Steven Whitehouse wrote:
Abhi noticed that we were getting a complaint from the RCU subsystem
about access of an RCU protected list under the write side bit lock.
This patch adds additional annotation to check both the RCU read
lock and the write side bit lock before printing a message.
Signed-off-by: Steven Whitehouse <swhiteho@xxxxxxxxxx>
Reported-by: Abhijith Das <adas@xxxxxxxxxx>
Tested-by: Abhijith Das <adas@xxxxxxxxxx>
Looks plausible to me on first glance, copying Nick Piggin and Christoph
Hellwig. If they have no objections, I will queue this.
Thanx, Paul
Has this had any attention yet? I'm also seeing the complaint quite
frequently:
[ 68.738811] ===============================
[ 68.741380] [ INFO: suspicious RCU usage. ]
[ 68.748785] 3.8.0-0.rc7.git1.1.fc19.x86_64 #1 Not tainted
[ 68.750841] -------------------------------
[ 68.752418] include/linux/rculist_bl.h:23 suspicious
rcu_dereference_check() usage!
[ 68.755264]
[ 68.755264] other info that might help us debug this:
[ 68.755264]
[ 68.758030]
[ 68.758030] rcu_scheduler_active = 1, debug_locks = 0
[ 68.760316] 1 lock held by mount/476:
[ 68.761896] #0: (&type->s_umount_key#38/1){+.+.+.}, at:
[<ffffffff811dbbee>] sget+0x39e/0x670
[ 68.767115]
[ 68.767115] stack backtrace:
[ 68.769529] Pid: 476, comm: mount Not tainted
3.8.0-0.rc7.git1.1.fc19.x86_64 #1
[ 68.772095] Call Trace:
[ 68.772995] [<ffffffff810d73b7>] lockdep_rcu_suspicious+0xe7/0x120
[ 68.775184] [<ffffffffa00e3238>] search_bucket+0x118/0x160 [gfs2]
[ 68.777559] [<ffffffffa00e47c3>] gfs2_glock_get+0x603/0x7b0 [gfs2]
[ 68.780749] [<ffffffffa00e41c5>] ? gfs2_glock_get+0x5/0x7b0 [gfs2]
[ 68.784173] [<ffffffffa00e6db9>] gfs2_glock_nq_num+0x29/0x90 [gfs2]
[ 68.786551] [<ffffffffa00f2b79>] gfs2_mount+0x869/0xf30 [gfs2]
[ 68.788672] [<ffffffff810ad428>] ? sched_clock_cpu+0xa8/0x100
[ 68.790739] [<ffffffff810d561d>] ? trace_hardirqs_off+0xd/0x10
[ 68.793042] [<ffffffff810ad56f>] ? local_clock+0x5f/0x70
[ 68.794940] [<ffffffff81702500>] ? __mutex_unlock_slowpath+0x80/0x170
[ 68.798236] [<ffffffff811dcb49>] mount_fs+0x39/0x1b0
[ 68.800409] [<ffffffff811879c0>] ? __alloc_percpu+0x10/0x20
[ 68.803692] [<ffffffff811fa8e3>] vfs_kern_mount+0x63/0xf0
[ 68.806773] [<ffffffff811fcfb5>] do_mount+0x205/0xa90
[ 68.809669] [<ffffffff8118c8ec>] ? might_fault+0x5c/0xb0
[ 68.812717] [<ffffffff811819fb>] ? strndup_user+0x4b/0xf0
[ 68.816066] [<ffffffff811fd8c3>] sys_mount+0x83/0xc0
[ 68.818284] [<ffffffff8170ead9>] system_call_fastpath+0x16/0x1b
It would be good to have this silenced for 3.8 but I think there's not
long to go.
Thanks,
Andy
diff --git a/include/linux/list_bl.h b/include/linux/list_bl.h
index 31f9d75..2eb8855 100644
--- a/include/linux/list_bl.h
+++ b/include/linux/list_bl.h
@@ -125,6 +125,11 @@ static inline void hlist_bl_unlock(struct hlist_bl_head *b)
__bit_spin_unlock(0, (unsigned long *)b);
}
+static inline bool hlist_bl_is_locked(struct hlist_bl_head *b)
+{
+ return bit_spin_is_locked(0, (unsigned long *)b);
+}
+
/**
* hlist_bl_for_each_entry - iterate over list of given type
* @tpos: the type * to use as a loop cursor.
diff --git a/include/linux/rculist_bl.h b/include/linux/rculist_bl.h
index cf1244f..4f216c5 100644
--- a/include/linux/rculist_bl.h
+++ b/include/linux/rculist_bl.h
@@ -20,7 +20,7 @@ static inline void hlist_bl_set_first_rcu(struct hlist_bl_head *h,
static inline struct hlist_bl_node *hlist_bl_first_rcu(struct hlist_bl_head *h)
{
return (struct hlist_bl_node *)
- ((unsigned long)rcu_dereference(h->first) & ~LIST_BL_LOCKMASK);
+ ((unsigned long)rcu_dereference_check(h->first, hlist_bl_is_locked(h)) & ~LIST_BL_LOCKMASK);
}
/**
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