linux-kernel - Re: [PATCH v3 0/10] Uprobes v3

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Date:	Thu, 13 May 2010 17:37:39 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Mel Gorman <mel@....ul.ie>,
	Randy Dunlap <rdunlap@...otime.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Roland McGrath <roland@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Mark Wielaard <mjw@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Rik van Riel <riel@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v3 0/10] Uprobes v3

> 
> Hrmm, you could do something like the above and use write_protect_page()
> along with that lock_page() you do to sync against concurrent faults. It
> won't be the fastest code around but it should work I guess.

Okay, thanks for the code.

> 
> Something like try_to_merge_one_page() in the KSM code:
> 
> write_opcode(struct mm_struct *mm, unsigned long address, void *insn,
> int len)
> {
> 	down_read(mm->mmap_sem);

[ snipped]
> 
> 	kunmap_atomic(vaddr_new);
> 	kunmap_atomic(vaddr_old);
> 
> 	/* XXX: frob mlock state */

I think you are referring to mlock_vma_page() and munlock_vma_page that
we have in try_to_merge_one_page(). However mlock_vma_page and
munlock_vma_page are not exposed outside mm as they are declared inside
mm/internal.h. So do you suggest moving the declarations out of
mm/internal.h or have a wrapper function defined in mm/ that could be
used by both KSM and uprobes.

> 
> 	/* flip pages, do_wp_page() will fail pte_same() and bail */
> 	err = replace_page(vma, new_page, old_page, orig_pte)
> 	if (err) goto fail_more;
> 
> 	/* we're done, let 'em rip */
> 	unlock_page(old_page);
> 	put_page(old_page);
> 
> 	return;
> 
> fail:
> 	/* XXX: fixup stuff */
> }
> 
> Note that this can fail for fun reasons like O_DIRECT IO, but that
> should be very rare indeed on text pages.
> 
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