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[85.193.35.108]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a868f48a77asm144168466b.180.2024.08.22.10.35.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Aug 2024 10:35:47 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Thu, 22 Aug 2024 19:35:45 +0200 To: Andrii Nakryiko Cc: Jiri Olsa , Andrii Nakryiko , linux-trace-kernel@vger.kernel.org, peterz@infradead.org, oleg@redhat.com, rostedt@goodmis.org, mhiramat@kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, paulmck@kernel.org, willy@infradead.org, surenb@google.com, akpm@linux-foundation.org, linux-mm@kvack.org Subject: Re: [PATCH v3 04/13] uprobes: travers uprobe's consumer list locklessly under SRCU protection Message-ID: References: <20240813042917.506057-1-andrii@kernel.org> <20240813042917.506057-5-andrii@kernel.org> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Thu, Aug 22, 2024 at 09:59:29AM -0700, Andrii Nakryiko wrote: > On Thu, Aug 22, 2024 at 7:22 AM Jiri Olsa wrote: > > > > On Mon, Aug 12, 2024 at 09:29:08PM -0700, Andrii Nakryiko wrote: > > > > SNIP > > > > > @@ -1125,18 +1103,31 @@ void uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc) > > > int err; > > > > > > down_write(&uprobe->register_rwsem); > > > - if (WARN_ON(!consumer_del(uprobe, uc))) { > > > - err = -ENOENT; > > > - } else { > > > - err = register_for_each_vma(uprobe, NULL); > > > - /* TODO : cant unregister? schedule a worker thread */ > > > - if (unlikely(err)) > > > - uprobe_warn(current, "unregister, leaking uprobe"); > > > - } > > > + > > > + list_del_rcu(&uc->cons_node); > > > > hi, > > I'm using this patchset as base for my changes and stumbled on this today, > > I'm probably missing something, but should we keep the 'uprobe->consumer_rwsem' > > lock around the list_del_rcu? > > > > Note that original code also didn't take consumer_rwsem, but rather > kept register_rwsem (which we still use). humm, consumer_del took consumer_rwsem, right? jirka > > There is a bit of mix of using register_rwsem and consumer_rwsem for > working with consumer list. Code hints at this as being undesirable > and "temporary", but you know, it's not broken :) > > Anyways, my point is that we didn't change the behavior, this should > be fine. That _rcu() in list_del_rcu() is not about lockless > modification of the list, but rather modification in such a way as to > keep lockless RCU-protected *readers* correct. It just does some more > memory barrier/release operations more carefully. > > > jirka > > > > > > > + err = register_for_each_vma(uprobe, NULL); > > > + > > > up_write(&uprobe->register_rwsem); > > > > > > - if (!err) > > > - put_uprobe(uprobe); > > > + /* TODO : cant unregister? schedule a worker thread */ > > > + if (unlikely(err)) { > > > + uprobe_warn(current, "unregister, leaking uprobe"); > > > + goto out_sync; > > > + } > > > + > > > + put_uprobe(uprobe); > > > +