Messages in this thread Patch in this message | | | Date | Sat, 10 May 2008 01:13:57 +0300 | From | Eduard - Gabriel Munteanu <> | Subject | Using markers w/ preemptible RCU in early code |
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Hello,
I'm working on the kmemtrace GSoC project and I'm having a little problem.
My code inserts probes during early code (just after kmem_cache_init()). This works on the classic RCU. But on the preemptible RCU, this triggers BUG()s (supposedly on each probe, there are two), although the kernel runs fine:
> BUG: scheduling while atomic: swapper/0/0x00000002 > Pid: 0, comm: swapper Not tainted 2.6.25-00002-gf80e324-dirty #16 > > Call Trace: > [<ffffffff802365f5>] __schedule_bug+0x65/0x70 > [<ffffffff804f8bb0>] thread_return+0x346/0x566 > [<ffffffff802734ba>] ? get_marker+0x23a/0x260 > [<ffffffff8025fbc6>] ? put_online_cpus+0x46/0x70 > [<ffffffff80270c88>] __synchronize_sched+0x48/0x80 > [<ffffffff802741a2>] marker_probe_register+0x152/0x660 > [<ffffffff8029af10>] ? kmemtrace_probe_alloc+0x0/0x1b0 > [<ffffffff8029ad6d>] kmemtrace_init+0x4d/0xd0 > [<ffffffff80693c05>] start_kernel+0x205/0x300 > [<ffffffff806931b2>] _sinittext+0x1b2/0x200
The is triggered by the following code in marker_probe_register(): #ifdef CONFIG_PREEMPT_RCU synchronize_sched(); /* Until we have the call_rcu_sched() */ #endif
Since preemption and SMP are disabled during early code, we could do something like: diff --git a/kernel/marker.c b/kernel/marker.c index 005b959..84964dc 100644 --- a/kernel/marker.c +++ b/kernel/marker.c @@ -23,6 +23,7 @@ #include <linux/rcupdate.h> #include <linux/marker.h> #include <linux/err.h> +#include <linux/hardirq.h> extern struct marker __start___markers[]; extern struct marker __stop___markers[]; @@ -672,7 +673,9 @@ int marker_probe_register(const char *name, const char *format, /* write rcu_pending before calling the RCU callback */ smp_wmb(); #ifdef CONFIG_PREEMPT_RCU - synchronize_sched(); /* Until we have the call_rcu_sched() */ + /* We are not preemptible when registering probes in early code */ + if (likely(preemptible())) + synchronize_sched(); /* Until we have the call_rcu_sched() */ #endif call_rcu(&entry->rcu, free_old_closure); end: Is this the best approach? marker_probe_register() isn't a hot path, so that check won't mess up the performance. Anyway, this works for me.
Eduard
(forgot LKML, added now.)
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