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Date: Tue, 27 Sep 2011 18:20:20 +0530
From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>, Steven Rostedt <rostedt@goodmis.org>,
        Linux-mm <linux-mm@kvack.org>,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Jonathan Corbet <corbet@lwn.net>, Hugh Dickins <hughd@google.com>,
        Christoph Hellwig <hch@infradead.org>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jim Keniston <jkenisto@linux.vnet.ibm.com>,
        Roland McGrath <roland@hack.frob.com>,
        Andi Kleen <andi@firstfloor.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v5 3.1.0-rc4-tip 18/26]   uprobes: slot allocation.
Message-ID: <20110927125020.GB3685@linux.vnet.ibm.com>
Reply-To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
References: <20110920115938.25326.93059.sendpatchset@srdronam.in.ibm.com>
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* Peter Zijlstra <peterz@infradead.org> [2011-09-27 14:37:59]:

> On Tue, 2011-09-20 at 17:33 +0530, Srikar Dronamraju wrote:
> > +static unsigned long xol_take_insn_slot(struct uprobes_xol_area *area)
> > +{
> > +       unsigned long slot_addr, flags;
> > +       int slot_nr;
> > +
> > +       do {
> > +               spin_lock_irqsave(&area->slot_lock, flags);
> > +               slot_nr = find_first_zero_bit(area->bitmap, UINSNS_PER_PAGE);
> > +               if (slot_nr < UINSNS_PER_PAGE) {
> > +                       __set_bit(slot_nr, area->bitmap);
> > +                       slot_addr = area->vaddr +
> > +                                       (slot_nr * UPROBES_XOL_SLOT_BYTES);
> > +                       atomic_inc(&area->slot_count);
> > +               }
> > +               spin_unlock_irqrestore(&area->slot_lock, flags);
> > +               if (slot_nr >= UINSNS_PER_PAGE)
> > +                       xol_wait_event(area);
> > +
> > +       } while (slot_nr >= UINSNS_PER_PAGE);
> > +
> > +       return slot_addr;
> > +} 
> 
> Why isn't a find_first_bit() + set_and_test_bit() not sufficient? That
> is, what do you need that lock for?

yes, we could do without the lock to.
Will do this in the next patchset.

-- 
Thanks and Regards 
Srikar