From: Oleg Nesterov <oleg@redhat.com>
To: Song Liu <songliubraving@fb.com>
Cc: lkml <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
"matthew.wilcox@oracle.com" <matthew.wilcox@oracle.com>,
"kirill.shutemov@linux.intel.com"
<kirill.shutemov@linux.intel.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"rostedt@goodmis.org" <rostedt@goodmis.org>,
Kernel Team <Kernel-team@fb.com>,
"william.kucharski@oracle.com" <william.kucharski@oracle.com>
Subject: Re: [PATCH v8 2/4] uprobe: use original page when all uprobes are removed
Date: Thu, 25 Jul 2019 10:14:14 +0200 [thread overview]
Message-ID: <20190725081414.GB4707@redhat.com> (raw)
In-Reply-To: <BCE000B2-3F72-4148-A75C-738274917282@fb.com>
On 07/24, Song Liu wrote:
>
>
> > On Jul 24, 2019, at 4:37 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> >
> > On 07/24, Song Liu wrote:
> >>
> >> lock_page(old_page);
> >> @@ -177,15 +180,24 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
> >> mmu_notifier_invalidate_range_start(&range);
> >> err = -EAGAIN;
> >> if (!page_vma_mapped_walk(&pvmw)) {
> >> - mem_cgroup_cancel_charge(new_page, memcg, false);
> >> + if (!orig)
> >> + mem_cgroup_cancel_charge(new_page, memcg, false);
> >> goto unlock;
> >> }
> >> VM_BUG_ON_PAGE(addr != pvmw.address, old_page);
> >>
> >> get_page(new_page);
> >> - page_add_new_anon_rmap(new_page, vma, addr, false);
> >> - mem_cgroup_commit_charge(new_page, memcg, false, false);
> >> - lru_cache_add_active_or_unevictable(new_page, vma);
> >> + if (orig) {
> >> + lock_page(new_page); /* for page_add_file_rmap() */
> >> + page_add_file_rmap(new_page, false);
> >
> >
> > Shouldn't we re-check new_page->mapping after lock_page() ? Or we can't
> > race with truncate?
>
> We can't race with truncate, because the file is open as binary and
> protected with DENYWRITE (ETXTBSY).
No. Yes, deny_write_access() protects mm->exe_file, but not the dynamic
libraries or other files which can be mmaped.
> > and I am worried this code can try to lock the same page twice...
> > Say, the probed application does MADV_DONTNEED and then writes "int3"
> > into vma->vm_file at the same address to fool verify_opcode().
> >
>
> Do you mean the case where old_page == new_page?
Yes,
> I think this won't
> happen, because in uprobe_write_opcode() we only do orig_page for
> !is_register case.
See above.
!is_register doesn't necessarily mean the original page was previously cow'ed.
And even if it was cow'ed, MADV_DONTNEED can restore the original mapping.
Oleg.
next prev parent reply other threads:[~2019-07-25 8:14 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-24 8:35 [PATCH v8 0/4] THP aware uprobe Song Liu
2019-07-24 8:35 ` [PATCH v8 1/4] mm: move memcmp_pages() and pages_identical() Song Liu
2019-07-24 8:35 ` [PATCH v8 2/4] uprobe: use original page when all uprobes are removed Song Liu
2019-07-24 9:07 ` Oleg Nesterov
2019-07-24 9:17 ` Oleg Nesterov
2019-07-24 9:20 ` Song Liu
2019-07-24 11:37 ` Oleg Nesterov
2019-07-24 18:52 ` Song Liu
2019-07-25 8:14 ` Oleg Nesterov [this message]
2019-07-25 18:17 ` Song Liu
2019-07-26 6:07 ` Song Liu
2019-07-26 8:44 ` Oleg Nesterov
2019-07-26 21:19 ` Song Liu
2019-07-24 8:35 ` [PATCH v8 3/4] mm, thp: introduce FOLL_SPLIT_PMD Song Liu
2019-07-24 8:36 ` [PATCH v8 4/4] uprobe: use FOLL_SPLIT_PMD instead of FOLL_SPLIT Song Liu
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