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Date: Fri, 3 Apr 2015 18:35:40 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Sasha Levin <sasha.levin@oracle.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm/memory: print also a_ops->readpage in print_bad_pte
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On Sat, 4 Apr 2015 03:47:12 +0300 Konstantin Khlebnikov <koct9i@gmail.com> wrote:

> On Sat, Apr 4, 2015 at 1:10 AM, Andrew Morton <akpm@linux-foundation.org> wrote:
> > On Fri, 03 Apr 2015 20:18:18 +0300 Konstantin Khlebnikov <khlebnikov@yandex-team.ru> wrote:
> >
> >> A lot of filesystems use generic_file_mmap() and filemap_fault(),
> >> f_op->mmap and vm_ops->fault aren't enough to identify filesystem.
> >>
> >> This prints file name, vm_ops->fault, f_op->mmap and a_ops->readpage
> >> (which is almost always implemented and filesystem-specific).
> >>
> >> Example:
> >>
> >> [   23.676410] BUG: Bad page map in process sh  pte:1b7e6025 pmd:19bbd067
> >> [   23.676887] page:ffffea00006df980 count:4 mapcount:1 mapping:ffff8800196426c0 index:0x97
> >> [   23.677481] flags: 0x10000000000000c(referenced|uptodate)
> >> [   23.677896] page dumped because: bad pte
> >> [   23.678205] addr:00007f52fcb17000 vm_flags:00000075 anon_vma:          (null) mapping:ffff8800196426c0 index:97
> >> [   23.678922] file:libc-2.19.so fault:filemap_fault mmap:generic_file_readonly_mmap readpage:v9fs_vfs_readpage
> >
> > Is that why we print these out?  Just to identify the fs type?
> >
> > There's always vma->vm_file->f_inode->i_sb->s_magic ;)
> 
> Yes, but that also might be anon inode/file mapped by some driver, so
> s_magic isn't enough.

Well, we could ensure that every file_system_type has a valid ->name.
Do an audit, put a debug check in register_filesystem()?