linux-kernel - Re: [PATCH 08/23] parisc: add pte_unmap() to balance get

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Message-ID: <6de39db5-d9aa-b35a-1652-8bdf90e7df72@google.com>
Date:   Sun, 14 May 2023 11:20:16 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Helge Deller <deller@....de>
cc:     Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Michal Simek <monstr@...str.eu>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        John David Anglin <dave.anglin@...l.net>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Alexandre Ghiti <alexghiti@...osinc.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        "David S. Miller" <davem@...emloft.net>,
        Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>, x86@...nel.org,
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        linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 08/23] parisc: add pte_unmap() to balance get_ptep()

On Sat, 13 May 2023, Helge Deller wrote:

> Hi Hugh,
> 
> On 5/10/23 06:52, Hugh Dickins wrote:
> > To keep balance in future, remember to pte_unmap() after a successful
> > get_ptep().  And (we might as well) pretend that flush_cache_pages()
> > really needed a map there, to read the pfn before "unmapping".
> >
> > Signed-off-by: Hugh Dickins <hughd@...gle.com>
> > ---
> >   arch/parisc/kernel/cache.c | 26 +++++++++++++++++++++-----
> >   1 file changed, 21 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/parisc/kernel/cache.c b/arch/parisc/kernel/cache.c
> > index 1d3b8bc8a623..b0c969b3a300 100644
> > --- a/arch/parisc/kernel/cache.c
> > +++ b/arch/parisc/kernel/cache.c
> > @@ -425,10 +425,15 @@ void flush_dcache_page(struct page *page)
> >     offset = (pgoff - mpnt->vm_pgoff) << PAGE_SHIFT;
> >     addr = mpnt->vm_start + offset;
> >     if (parisc_requires_coherency()) {
> > +			bool needs_flush = false;
> >      pte_t *ptep;
> >
> >   			ptep = get_ptep(mpnt->vm_mm, addr);
> > -			if (ptep && pte_needs_flush(*ptep))
> > +			if (ptep) {
> > +				needs_flush = pte_needs_flush(*ptep);
> > +				pte_unmap(ptep);
> > +			}
> > +			if (needs_flush)
> >     		flush_user_cache_page(mpnt, addr);
> >     } else {
> >   			/*
> > @@ -560,14 +565,20 @@ EXPORT_SYMBOL(flush_kernel_dcache_page_addr);
> >   static void flush_cache_page_if_present(struct vm_area_struct *vma,
> >   	unsigned long vmaddr, unsigned long pfn)
> >   {
> > -	pte_t *ptep = get_ptep(vma->vm_mm, vmaddr);
> > +	bool needs_flush = false;
> > +	pte_t *ptep;
> >
> >    /*
> >     * The pte check is racy and sometimes the flush will trigger
> >     * a non-access TLB miss. Hopefully, the page has already been
> >     * flushed.
> >     */
> > -	if (ptep && pte_needs_flush(*ptep))
> > +	ptep = get_ptep(vma->vm_mm, vmaddr);
> > +	if (ptep) {
> > +		needs_flush = pte_needs_flush(*ptep))
> 
> ^^^^^
> One ")" too much and lacks a trailing ";"
> Should be:
> 		needs_flush = pte_needs_flush(*ptep);
> 
> With that fixed the kernel compiles and boots sucessfully on parisc.

Urgh! Indeed, thanks a lot Helge: I'll fold that in.

Hugh