linux-kernel - Re: debugctl msr

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Date:	Fri, 14 Nov 2008 22:10:35 +0100
From:	"stephane eranian" <eranian@...glemail.com>
To:	"Metzger, Markus T" <markus.t.metzger@...el.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>, "Andi Kleen" <andi@...stfloor.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	"Markus Metzger" <markus.t.metzger@...glemail.com>
Subject: Re: debugctl msr

Markus,


I am trying another approach for connecting perfmon to ds.c. I have
added new callbacks
to perfmon to allow me to invoke ds_request_pebs, once I know the
target thread or CPU.
That seems to work, however I ran into a spinlock problem is ds_request():

static int ds_request(struct task_struct *task, void *base, size_t size,
                      ds_ovfl_callback_t ovfl, enum ds_qualifier qual)
{
        struct ds_context *context;
        unsigned long buffer, adj;
        const unsigned long alignment = (1 << 3);
        int error = 0;

        if (!ds_cfg.sizeof_ds)
                return -EOPNOTSUPP;

        /* we require some space to do alignment adjustments below */
        if (size < (alignment + ds_cfg.sizeof_rec[qual]))
                return -EINVAL;

        /* buffer overflow notification is not yet implemented */
        if (ovfl)
                return -EOPNOTSUPP;


        spin_lock(&ds_lock);

>>        if (!check_tracer(task))
>>                return -EPERM;

You need to spin_unlock() before returning here!
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