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Howlett" , Vlastimil Babka , Jann Horn , linux-mm@kvack.org, Peng Zhang Subject: Re: [PATCH] fork: avoid inappropriate uprobe access to invalid mm Message-ID: <20241210172315.GC31266@redhat.com> References: <20241210163104.55181-1-lorenzo.stoakes@oracle.com> <20241210165334.GB31266@redhat.com> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241210165334.GB31266@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 On 12/10, Oleg Nesterov wrote: > > I must have missed something, but... > > On 12/10, Lorenzo Stoakes wrote: > > > > @@ -1746,9 +1741,11 @@ static struct mm_struct *dup_mm(struct task_struct *tsk, > > if (!mm_init(mm, tsk, mm->user_ns)) > > goto fail_nomem; > > > > + uprobe_start_dup_mmap(); > > err = dup_mmap(mm, oldmm); > > if (err) > > - goto free_pt; > > + goto free_pt_end_uprobe; > > + uprobe_end_dup_mmap(); > > > > mm->hiwater_rss = get_mm_rss(mm); > > mm->hiwater_vm = mm->total_vm; > > @@ -1758,6 +1755,8 @@ static struct mm_struct *dup_mm(struct task_struct *tsk, > > > > return mm; > > > > +free_pt_end_uprobe: > > + uprobe_end_dup_mmap(); > > if dup_mmap() fails and "mm" is incomplete, then with this version dup_mmap_sem > is dropped before __mmput/exit_mmap/etc. How can this help? Easy to fix, but what ensures that another mmget(mm) is not possible until dup_mm() calls mmput() and drops dup_mmap_sem? Sorry, my understanding of mm/ is very limited... Oleg.