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From:   Naoya Horiguchi <naoya.horiguchi@linux.dev>
To:     Yang Shi <shy828301@gmail.com>
Cc:     HORIGUCHI =?utf-8?B?TkFPWUEo5aCA5Y+jIOebtOS5nyk=?= 
        <naoya.horiguchi@nec.com>, Hugh Dickins <hughd@google.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Matthew Wilcox <willy@infradead.org>,
        Peter Xu <peterx@redhat.com>,
        Oscar Salvador <osalvador@suse.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux MM <linux-mm@kvack.org>,
        Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [v4 PATCH 5/6] mm: shmem: don't truncate page if memory failure
 happens
Message-ID: <20211019223007.GA2324358@u2004>
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On Tue, Oct 19, 2021 at 10:29:51AM -0700, Yang Shi wrote:
> On Mon, Oct 18, 2021 at 10:52 PM Naoya Horiguchi
> <naoya.horiguchi@linux.dev> wrote:
> >
> > On Thu, Oct 14, 2021 at 12:16:14PM -0700, Yang Shi wrote:
...
> > > @@ -2466,7 +2467,15 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
> > >                       return -EPERM;
> > >       }
> > >
> > > -     return shmem_getpage(inode, index, pagep, SGP_WRITE);
> > > +     ret = shmem_getpage(inode, index, pagep, SGP_WRITE);
> > > +
> > > +     if (*pagep && PageHWPoison(*pagep)) {
> >
> > shmem_getpage() could return with pagep == NULL, so you need check ret first
> > to avoid NULL pointer dereference.
> 
> Realy? IIUC pagep can't be NULL. It is a pointer's pointer passed in
> by the caller, for example, generic_perform_write(). Of course,
> "*pagep" could be NULL.

Oh, I simply missed this. You're right. Please ignore my comment on this.

- Naoya Horiguchi