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Sun, 27 Apr 2025 10:14:25 -0400 X-MC-Unique: NkxcXgFHPNizLPHKlO-eyQ-1 X-Mimecast-MFC-AGG-ID: NkxcXgFHPNizLPHKlO-eyQ_1745763263 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A589C19560AA; Sun, 27 Apr 2025 14:14:21 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.224.18]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 645D1180045C; Sun, 27 Apr 2025 14:14:15 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Sun, 27 Apr 2025 16:13:43 +0200 (CEST) Date: Sun, 27 Apr 2025 16:13:35 +0200 From: Oleg Nesterov To: Jiri Olsa Cc: Peter Zijlstra , Andrii Nakryiko , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, x86@kernel.org, Song Liu , Yonghong Song , John Fastabend , Hao Luo , Steven Rostedt , Masami Hiramatsu , Alan Maguire , David Laight , Thomas =?iso-8859-1?Q?Wei=DFschuh?= , Ingo Molnar Subject: Re: [PATCH perf/core 03/22] uprobes: Move ref_ctr_offset update out of uprobe_write_opcode Message-ID: <20250427141335.GA9350@redhat.com> References: <20250421214423.393661-1-jolsa@kernel.org> <20250421214423.393661-4-jolsa@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=us-ascii Content-Disposition: inline In-Reply-To: <20250421214423.393661-4-jolsa@kernel.org> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 On 04/21, Jiri Olsa wrote: > > +static int set_swbp_refctr(struct uprobe *uprobe, struct vm_area_struct *vma, unsigned long vaddr) > +{ > + struct mm_struct *mm = vma->vm_mm; > + int err; > + > + /* We are going to replace instruction, update ref_ctr. */ > + if (uprobe->ref_ctr_offset) { > + err = update_ref_ctr(uprobe, mm, 1); > + if (err) > + return err; > + } > + > + err = set_swbp(&uprobe->arch, vma, vaddr); > + > + /* Revert back reference counter if instruction update failed. */ > + if (err && uprobe->ref_ctr_offset) > + update_ref_ctr(uprobe, mm, -1); > + return err; > } ... > +static int set_orig_refctr(struct uprobe *uprobe, struct vm_area_struct *vma, unsigned long vaddr) > +{ > + int err = set_orig_insn(&uprobe->arch, vma, vaddr); > + > + /* Revert back reference counter even if instruction update failed. */ > + if (uprobe->ref_ctr_offset) > + update_ref_ctr(uprobe, vma->vm_mm, -1); > + return err; > } This doesn't look right even in the simplest case... To simplify, suppose that uprobe_register() needs to change a single mm/vma and set_swbp() fails. In this case uprobe_register() calls uprobe_unregister() which will find the same vma and call set_orig_refctr(). set_orig_insn() will do nothing. But update_ref_ctr(uprobe, vma->vm_mm, -1) is wrong/unbalanced. The current code updates ref_ctr after the verify_opcode() check, so it doesn't have this problem. ------------------------------------------------------------------------------- OTOH, I think that the current logic is not really correct too, /* Revert back reference counter if instruction update failed. */ if (ret < 0 && is_register && ref_ctr_updated) update_ref_ctr(uprobe, mm, -1); I think that "Revert back reference counter" logic should not depend on is_register. Otherwise we can have the unbalanced update_ref_ctr(-1) if uprobe_unregister() fails, then another uprobe_register() comes at the same address, and after that uprobe_unregister() succeeds. Oleg.