linux-kernel - Re: [PATCH 2/2] ftrace: release functions from hash

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Date:	Tue, 21 Oct 2008 14:27:55 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	linux-kernel@...r.kernel.org
cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 2/2] ftrace: release functions from hash



Ingo,

I found a bug with this patch. Do not incorporate it. I'll come up
with a new patch to replace this one.

Thanks,

-- Steve

On Tue, 21 Oct 2008, Steven Rostedt wrote:

> The x86 architecture uses a static recording of mcount caller locations
> and is not affected by this patch.
> 
> For architectures still using the dynamic ftrace daemon, this patch is
> critical. It removes the race between the recording of a function that
> calls mcount, the unloading of a module, and the ftrace daemon updating
> the call sites.
> 
> This patch adds the releasing of the hash functions that the daemon uses
> to update the mcount call sites. When a module is unloaded, not only
> are the replaced call site table update, but now so is the hash recorded
> functions that the ftrace daemon will use.
> 
> Again, architectures that implement MCOUNT_RECORD are not affected by
> this (which currently only x86 has).
> 
> Signed-off-by: Steven Rostedt <srostedt@...hat.com>
> ---
>  kernel/trace/ftrace.c |   44 ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 44 insertions(+)
> 
> Index: linux-compile.git/kernel/trace/ftrace.c
> ===================================================================
> --- linux-compile.git.orig/kernel/trace/ftrace.c	2008-10-21 09:34:51.000000000 -0400
> +++ linux-compile.git/kernel/trace/ftrace.c	2008-10-21 10:31:24.000000000 -0400
> @@ -164,10 +164,14 @@ static DEFINE_SPINLOCK(ftrace_hash_lock)
>  #define ftrace_hash_lock(flags)	  spin_lock_irqsave(&ftrace_hash_lock, flags)
>  #define ftrace_hash_unlock(flags) \
>  			spin_unlock_irqrestore(&ftrace_hash_lock, flags)
> +static void ftrace_release_hash(unsigned long start, unsigned long end);
>  #else
>  /* This is protected via the ftrace_lock with MCOUNT_RECORD. */
>  #define ftrace_hash_lock(flags)   do { (void)(flags); } while (0)
>  #define ftrace_hash_unlock(flags) do { } while(0)
> +static inline void ftrace_release_hash(unsigned long start, unsigned long end)
> +{
> +}
>  #endif
>  
>  /*
> @@ -354,6 +358,8 @@ void ftrace_release(void *start, unsigne
>  		}
>  	}
>  	spin_unlock(&ftrace_lock);
> +
> +	ftrace_release_hash(s, e);
>  }
>  
>  static struct dyn_ftrace *ftrace_alloc_dyn_node(unsigned long ip)
> @@ -1686,6 +1692,44 @@ void __init ftrace_init(void)
>  	ftrace_disabled = 1;
>  }
>  #else /* CONFIG_FTRACE_MCOUNT_RECORD */
> +
> +static void ftrace_release_hash(unsigned long start, unsigned long end)
> +{
> +	struct dyn_ftrace *rec;
> +	struct hlist_node *t, *n;
> +	struct hlist_head *head, temp_list;
> +	unsigned long flags;
> +	int i, cpu;
> +
> +	preempt_disable_notrace();
> +
> +	/* disable incase we call something that calls mcount */
> +	cpu = raw_smp_processor_id();
> +	per_cpu(ftrace_shutdown_disable_cpu, cpu)++;
> +
> +	ftrace_hash_lock(flags);
> +
> +	for (i = 0; i < FTRACE_HASHSIZE; i++) {
> +		INIT_HLIST_HEAD(&temp_list);
> +		head = &ftrace_hash[i];
> +
> +		/* all CPUS are stopped, we are safe to modify code */
> +		hlist_for_each_entry_safe(rec, t, n, head, node) {
> +			if (rec->flags & FTRACE_FL_FREE)
> +				continue;
> +
> +			if ((rec->ip >= start) && (rec->ip < end))
> +				ftrace_free_rec(rec);
> +		}
> +	}
> +
> +	ftrace_hash_unlock(flags);
> +
> +	per_cpu(ftrace_shutdown_disable_cpu, cpu)--;
> +	preempt_enable_notrace();
> +
> +}
> +
>  static int ftraced(void *ignore)
>  {
>  	unsigned long usecs;
> 
> -- 
> 
> 
--
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