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[2001:1ae9:1c2:4c00:726e:c10f:8833:ff22]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42d9b189a6asm15595165e9.38.2024.09.13.01.23.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Sep 2024 01:23:10 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Fri, 13 Sep 2024 10:22:56 +0200 To: Oleg Nesterov Cc: Peter Zijlstra , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , bpf@vger.kernel.org, Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Steven Rostedt , Masami Hiramatsu , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCHv3 1/7] uprobe: Add support for session consumer Message-ID: References: <20240909074554.2339984-1-jolsa@kernel.org> <20240909074554.2339984-2-jolsa@kernel.org> <20240912162028.GD27648@redhat.com> 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=us-ascii Content-Disposition: inline In-Reply-To: <20240912162028.GD27648@redhat.com> On Thu, Sep 12, 2024 at 06:20:29PM +0200, Oleg Nesterov wrote: > On 09/09, Jiri Olsa wrote: > > > > static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs) > > { > > struct uprobe_consumer *uc; > > int remove = UPROBE_HANDLER_REMOVE; > > - bool need_prep = false; /* prepare return uprobe, when needed */ > > + struct return_consumer *ric = NULL; > > + struct return_instance *ri = NULL; > > bool has_consumers = false; > > > > current->utask->auprobe = &uprobe->arch; > > > > list_for_each_entry_srcu(uc, &uprobe->consumers, cons_node, > > srcu_read_lock_held(&uprobes_srcu)) { > > + __u64 cookie = 0; > > int rc = 0; > > > > if (uc->handler) { > > - rc = uc->handler(uc, regs); > > - WARN(rc & ~UPROBE_HANDLER_MASK, > > + rc = uc->handler(uc, regs, &cookie); > > + WARN(rc < 0 || rc > 2, > > "bad rc=0x%x from %ps()\n", rc, uc->handler); > > } > > > > - if (uc->ret_handler) > > - need_prep = true; > > - > > + /* > > + * The handler can return following values: > > + * 0 - execute ret_handler (if it's defined) > > + * 1 - remove uprobe > > + * 2 - do nothing (ignore ret_handler) > > + */ > > remove &= rc; > > has_consumers = true; > > + > > + if (rc == 0 && uc->ret_handler) { > > should we enter this block if uc->handler == NULL? yes, consumer can have just ret_handler defined > > > + /* > > + * Preallocate return_instance object optimistically with > > + * all possible consumers, so we allocate just once. > > + */ > > + if (!ri) { > > + ri = alloc_return_instance(uprobe->consumers_cnt); > > This doesn't look right... > > Suppose we have a single consumer C1, so uprobe->consumers_cnt == 1 and > alloc_return_instance() allocates return_instance with for a single consumer, > so that only ri->consumers[0] is valid. > > Right after that uprobe_register()->consumer_add() adds another consumer > C2 with ->ret_handler != NULL. > > On the next iteration return_consumer_next() will return the invalid addr > == &ri->consumers[1]. > > perhaps this needs krealloc() ? damn.. there used to be a lock ;-) ok, for some reason I thought we are safe in that list iteration and we are not.. I just made selftest that triggers that I'm not sure the realloc will help, I feel like we need to allocate return consumer for each called handler separately to be safe > > > + if (!ri) > > + return; > > Not sure we should simply return if kzalloc fails... at least it would be better > to clear current->utask->auprobe. > > > + if (ri && !remove) > > + prepare_uretprobe(uprobe, regs, ri); /* put bp at return */ > > + else > > + kfree(ri); > > Well, if ri != NULL then remove is not possible, afaics... ri != NULL means > that at least one ->handler() returned rc = 0, thus "remove" must be zero. > > So it seems you can just do > > if (ri) > prepare_uretprobe(...); true, I think that should be enough thanks, jirka > > > Didn't read other parts of your patch yet ;) > > Oleg. >