From: Hugh Dickins <hughd@google.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
"Paul E. McKenney" <paul.mckenney@linaro.org>
Subject: Re: linux-next ppc64: RCU mods cause __might_sleep BUGs
Date: Wed, 2 May 2012 13:25:30 -0700 (PDT) [thread overview]
Message-ID: <alpine.LSU.2.00.1205021324430.24246@eggly.anvils> (raw)
In-Reply-To: <20120501232516.GR2441@linux.vnet.ibm.com>
On Tue, 1 May 2012, Paul E. McKenney wrote:
> > > > > On Mon, 2012-04-30 at 15:37 -0700, Hugh Dickins wrote:
> > > > > >
> > > > > > BUG: sleeping function called from invalid context at include/linux/pagemap.h:354
> > > > > > in_atomic(): 0, irqs_disabled(): 0, pid: 6886, name: cc1
> > > > > > Call Trace:
> > > > > > [c0000001a99f78e0] [c00000000000f34c] .show_stack+0x6c/0x16c (unreliable)
> > > > > > [c0000001a99f7990] [c000000000077b40] .__might_sleep+0x11c/0x134
> > > > > > [c0000001a99f7a10] [c0000000000c6228] .filemap_fault+0x1fc/0x494
> > > > > > [c0000001a99f7af0] [c0000000000e7c9c] .__do_fault+0x120/0x684
> > > > > > [c0000001a99f7c00] [c000000000025790] .do_page_fault+0x458/0x664
> > > > > > [c0000001a99f7e30] [c000000000005868] handle_page_fault+0x10/0x30
Got it at last. Embarrassingly obvious. __rcu_read_lock() and
__rcu_read_unlock() are not safe to be using __this_cpu operations,
the cpu may change in between the rmw's read and write: they should
be using this_cpu operations (or, I put preempt_disable/enable in the
__rcu_read_unlock below). __this_cpus there work out fine on x86,
which was given good instructions to use; but not so well on PowerPC.
I've been running successfully for an hour now with the patch below;
but I expect you'll want to consider the tradeoffs, and may choose a
different solution.
Hugh
--- 3.4-rc4-next-20120427/include/linux/rcupdate.h 2012-04-28 09:26:38.000000000 -0700
+++ testing/include/linux/rcupdate.h 2012-05-02 11:46:06.000000000 -0700
@@ -159,7 +159,7 @@ DECLARE_PER_CPU(struct task_struct *, rc
*/
static inline void __rcu_read_lock(void)
{
- __this_cpu_inc(rcu_read_lock_nesting);
+ this_cpu_inc(rcu_read_lock_nesting);
barrier(); /* Keep code within RCU read-side critical section. */
}
--- 3.4-rc4-next-20120427/kernel/rcupdate.c 2012-04-28 09:26:40.000000000 -0700
+++ testing/kernel/rcupdate.c 2012-05-02 11:44:13.000000000 -0700
@@ -72,6 +72,7 @@ DEFINE_PER_CPU(struct task_struct *, rcu
*/
void __rcu_read_unlock(void)
{
+ preempt_disable();
if (__this_cpu_read(rcu_read_lock_nesting) != 1)
__this_cpu_dec(rcu_read_lock_nesting);
else {
@@ -83,13 +84,14 @@ void __rcu_read_unlock(void)
barrier(); /* ->rcu_read_unlock_special load before assign */
__this_cpu_write(rcu_read_lock_nesting, 0);
}
-#ifdef CONFIG_PROVE_LOCKING
+#if 1 /* CONFIG_PROVE_LOCKING */
{
int rln = __this_cpu_read(rcu_read_lock_nesting);
- WARN_ON_ONCE(rln < 0 && rln > INT_MIN / 2);
+ BUG_ON(rln < 0 && rln > INT_MIN / 2);
}
#endif /* #ifdef CONFIG_PROVE_LOCKING */
+ preempt_enable();
}
EXPORT_SYMBOL_GPL(__rcu_read_unlock);
--- 3.4-rc4-next-20120427/kernel/sched/core.c 2012-04-28 09:26:40.000000000 -0700
+++ testing/kernel/sched/core.c 2012-05-01 22:40:46.000000000 -0700
@@ -2024,7 +2024,7 @@ asmlinkage void schedule_tail(struct tas
{
struct rq *rq = this_rq();
- rcu_switch_from(prev);
+ /* rcu_switch_from(prev); */
rcu_switch_to();
finish_task_switch(rq, prev);
@@ -7093,6 +7093,10 @@ void __might_sleep(const char *file, int
"BUG: sleeping function called from invalid context at %s:%d\n",
file, line);
printk(KERN_ERR
+ "cpu=%d preempt_count=%x preempt_offset=%x rcu_nesting=%x nesting_save=%x\n",
+ raw_smp_processor_id(), preempt_count(), preempt_offset,
+ rcu_preempt_depth(), current->rcu_read_lock_nesting_save);
+ printk(KERN_ERR
"in_atomic(): %d, irqs_disabled(): %d, pid: %d, name: %s\n",
in_atomic(), irqs_disabled(),
current->pid, current->comm);
next prev parent reply other threads:[~2012-05-02 20:25 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-30 22:37 linux-next ppc64: RCU mods cause __might_sleep BUGs Hugh Dickins
2012-04-30 23:14 ` Paul E. McKenney
2012-05-01 0:33 ` Benjamin Herrenschmidt
2012-05-01 5:10 ` Hugh Dickins
2012-05-01 14:22 ` Paul E. McKenney
2012-05-01 21:42 ` Hugh Dickins
2012-05-01 23:25 ` Paul E. McKenney
2012-05-02 20:25 ` Hugh Dickins [this message]
2012-05-02 20:49 ` Paul E. McKenney
2012-05-02 21:32 ` Paul E. McKenney
2012-05-02 21:36 ` Paul E. McKenney
2012-05-02 21:20 ` Benjamin Herrenschmidt
2012-05-02 21:54 ` Paul E. McKenney
2012-05-02 22:54 ` Hugh Dickins
2012-05-03 0:14 ` Paul E. McKenney
2012-05-03 0:24 ` Hugh Dickins
2012-05-07 16:21 ` Hugh Dickins
2012-05-07 18:50 ` Paul E. McKenney
2012-05-07 21:38 ` Hugh Dickins
2012-05-01 13:39 ` Paul E. McKenney
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