linux-kernel - Re: [v3 05/10] mmap locking API: Checking the Coccinelle software

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Message-ID: <590dbec7-341a-3480-dd47-cb3c65b023c7@web.de>
Date:   Sat, 28 Mar 2020 14:20:20 +0100
From:   Markus Elfring <Markus.Elfring@....de>
To:     Michel Lespinasse <walken@...gle.com>,
        Coccinelle <cocci@...teme.lip6.fr>, linux-mm@...ck.org
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        Liam Howlett <Liam.Howlett@...cle.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        David Rientjes <rientjes@...gle.com>,
        Hugh Dickins <hughd@...gle.com>, Ying Han <yinghan@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [v3 05/10] mmap locking API: Checking the Coccinelle software

>> How will corresponding software development resources evolve?
>
> I don't think I understand the question, or, actually, are you asking
> me or the coccinelle developers ?

I hope that another communication approach can eventually increase
the chances for a better common understanding of development challenges.

The code from a mentioned source file can be reduced to the following
test file.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/mips/mm/fault.c?id=69c5eea3128e775fd3c70ecf0098105d96dee330#n34

// deleted part
static void __kprobes __do_page_fault(struct pt_regs *regs, unsigned long write,
	unsigned long address)
{
	struct vm_area_struct * vma = NULL;
	struct task_struct *tsk = current;
	struct mm_struct *mm = tsk->mm;
// deleted part
retry:
	down_read(&mm->mmap_sem);
	vma = find_vma(mm, address);
	if (!vma)
		goto bad_area;
// deleted part
}
// deleted part


Application of the software “Coccinelle 1.0.8-00029-ga549b9f0” (OCaml 4.10.0)

elfring@...ne:~/Projekte/Coccinelle/Probe> spatch --parse-c do_page_fault-excerpt3.c
…
NB total files = 1; perfect = 1; pbs = 0; timeout = 0; =========> 100%
nb good = 15,  nb passed = 1 =========> 6.25% passed
nb good = 15,  nb bad = 0 =========> 100.00% good or passed


The discussed transformation approach can also be reduced for a test
to the following script for the semantic patch language.

@replacement@
expression x;
@@
-down_read
+mmap_read_lock
 (
- &
  x
- ->mmap_sem
 )


elfring@...ne:~/Projekte/Coccinelle/Probe> spatch use_mmap_locking_API_3.cocci do_page_fault-excerpt3.c


The desired diff is not generated so far.
How would you like to fix this situation?

Regards,
Markus