From nobody Mon Jul 15 18:33:23 2024 X-Original-To: dev-commits-src-all@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id 4WN9nZ653qz5RRJV; Mon, 15 Jul 2024 18:33:38 +0000 (UTC) (envelope-from mjguzik@gmail.com) Received: from mail-ed1-x531.google.com (mail-ed1-x531.google.com [IPv6:2a00:1450:4864:20::531]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (2048 bits) client-digest SHA256) (Client CN "smtp.gmail.com", Issuer "WR4" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4WN9nZ5LpSz4NWY; Mon, 15 Jul 2024 18:33:38 +0000 (UTC) (envelope-from mjguzik@gmail.com) Authentication-Results: mx1.freebsd.org; none Received: by mail-ed1-x531.google.com with SMTP id 4fb4d7f45d1cf-58be2b8b6b2so5872401a12.3; Mon, 15 Jul 2024 11:33:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1721068417; x=1721673217; darn=freebsd.org; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=xF1hyUVdsj3LgPWBbm/9cuYRl0QMg1woOnLVTjx/o84=; b=lsRYuYU8c3BJPn2aXq2Yyv7ipRuUaUcwa4+u7mcmsg6Xm5rAQbTdqzLxjypOIq8UDs 4Di3QMwkBYkGIkURsIx4ZwsLbicT4URBoTtbiCfHsXD/2uCCHzbghZppOUizvH50irHd 4ng5rA3BgkHLDacjqublHaPje2XELpa7F/kS9W/LeI/m7URfqU4yMcDSKEbX5SJMwt9X sIcjECelO5lmG6mX05mOu0b9kM+8kw8bNB3xGI7m56RyNx2nBGLuUo2XwwFYBZ6excD/ 1MMD5PbxK1luxotYsVv1l+xWxayqepQjJgZwWCuZPya1g3pUAMSEZOHAp43NpII02i9e ZfFA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1721068417; x=1721673217; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=xF1hyUVdsj3LgPWBbm/9cuYRl0QMg1woOnLVTjx/o84=; b=QxqrJIM5IF8Pf5i3bnX+v98fKQSwEH3GVNhikPrIUl1gQLdWOOu68IYq2b6GfNlz76 me/uw6IgNxRU4KvEruxwMhMcW0ptSrE/lGi9AYXSyBrJjRlmYqTcRLFwtmSuBJCe0cen SA8NEnu6XjvRdJrAPqWwd+0xgix3+KlwsTk2eCmawhHLPqyFpMK791rN2ILx3AlZ19s3 cD+nCNFQJOlLcZroT+ZYCKbJOpe1Cyka6Qc7Ohjt6r/YTXFDLeELflvT1wAvjgzuI+lE NEUK8OQ1wORK8Yjm7kXan+sakO0Kpy4pXZchP3goHgbEWqQNuwN6Dgcm/xvO5g+whSbY jAig== X-Forwarded-Encrypted: i=1; AJvYcCUmryvIzhqg6Jstn9p6UBHCmSxlevv5BVyzEscWQjibE9XUi5VFtuYkh6WiMxWTcOHl38M8EtWAW0VDKIZS97g+P0E/5nmlnyrmnEEI7EiWBlsKcHYWKNc6Wz4JTy3OdK7rptLaN4R4I5BLfDwRR96sgO2hMlgHpbBUNAk3s+A1MbQxcND7cmlMVePaZGU= X-Gm-Message-State: AOJu0Yxz7QWyXg3B+ZZJkty3eouzOd4nmqpXXCJ4KObx24Z5ffm0JJHg E9vB/doP4BSuxQdLjl0Sqn3JneQcjKKMIWxTBRNwaiqaoALLTjamenmtMNIH2nOI2jwZmxSplsg rBAnSeJN/cZ75KURRU+c8oRTt+FtnnvuF X-Google-Smtp-Source: AGHT+IFKGsKaBB/nLKGr+DS41fZ9h1zdnSGvo/+C+yC5j84C3Uuhe4F5uyAnXpMxljcVMY8aUdLeS+IQAYigzpsQU0s= X-Received: by 2002:a17:906:7311:b0:a72:81f5:85b6 with SMTP id a640c23a62f3a-a79e6a48054mr48428466b.18.1721068416843; Mon, 15 Jul 2024 11:33:36 -0700 (PDT) List-Id: Commit messages for all branches of the src repository List-Archive: https://lists.freebsd.org/archives/dev-commits-src-all List-Help: List-Post: List-Subscribe: List-Unsubscribe: X-BeenThere: dev-commits-src-all@freebsd.org Sender: owner-dev-commits-src-all@FreeBSD.org MIME-Version: 1.0 References: <202407111107.46BB7uSb007077@gitrepo.freebsd.org> <81cfe7ad-cbee-4122-abef-e47ce2b34f05@FreeBSD.org> In-Reply-To: From: Mateusz Guzik Date: Mon, 15 Jul 2024 20:33:23 +0200 Message-ID: Subject: Re: git: 87ee63bac69d - main - locks: add a runtime check for missing turnstile To: John Baldwin Cc: Mateusz Guzik , src-committers@freebsd.org, dev-commits-src-all@freebsd.org, dev-commits-src-main@freebsd.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Spamd-Bar: ---- X-Rspamd-Pre-Result: action=no action; module=replies; Message is reply to one we originated X-Spamd-Result: default: False [-4.00 / 15.00]; REPLY(-4.00)[]; ASN(0.00)[asn:15169, ipnet:2a00:1450::/32, country:US] X-Rspamd-Queue-Id: 4WN9nZ5LpSz4NWY On Mon, Jul 15, 2024 at 8:21=E2=80=AFPM John Baldwin wrot= e: > > On 7/15/24 13:59, Mateusz Guzik wrote: > > On Mon, Jul 15, 2024 at 6:22=E2=80=AFPM John Baldwin = wrote: > >> > >> On 7/11/24 07:07, Mateusz Guzik wrote: > >>> The branch main has been updated by mjg: > >>> > >>> URL: https://cgit.FreeBSD.org/src/commit/?id=3D87ee63bac69dc49291f555= 90b8baa57cad6c7d85 > >>> > >>> commit 87ee63bac69dc49291f55590b8baa57cad6c7d85 > >>> Author: Mateusz Guzik > >>> AuthorDate: 2024-07-11 00:17:27 +0000 > >>> Commit: Mateusz Guzik > >>> CommitDate: 2024-07-11 11:06:52 +0000 > >>> > >>> locks: add a runtime check for missing turnstile > >>> > >>> There are sometimes bugs which result in the unlock fast path f= ailing, > >>> which in turns causes a not-helpful crash report when dereferen= cing a > >>> NULL turnstile. Help debugging such cases by pointing out what = happened > >>> along with some debug. > >>> > >>> Sponsored by: Rubicon Communications, LLC ("Netgate") > >>> --- > >>> sys/kern/kern_mutex.c | 4 +++- > >>> sys/kern/kern_rwlock.c | 16 ++++++++++++---- > >>> 2 files changed, 15 insertions(+), 5 deletions(-) > >>> > >>> diff --git a/sys/kern/kern_mutex.c b/sys/kern/kern_mutex.c > >>> index 90361b23c09a..0fa624cc4bb1 100644 > >>> --- a/sys/kern/kern_mutex.c > >>> +++ b/sys/kern/kern_mutex.c > >>> @@ -1053,7 +1053,9 @@ __mtx_unlock_sleep(volatile uintptr_t *c, uintp= tr_t v) > >>> turnstile_chain_lock(&m->lock_object); > >>> _mtx_release_lock_quick(m); > >>> ts =3D turnstile_lookup(&m->lock_object); > >>> - MPASS(ts !=3D NULL); > >>> + if (__predict_false(ts =3D=3D NULL)) { > >>> + panic("got NULL turnstile on mutex %p v %zx", m, v); > >>> + } > >> > >> Hmm, this is just an expanded KASSERT() but always on rather than cond= itional on INVARIANTS? > >> > >> Do you have examples of the type of bugs that cause this? (Is it unlo= cking a freed mutex > >> or the like?) We generally hide all these types of checks under INVAR= IANTS rather than > >> shipping them in release kernels. > >> > > > > Use-after-free, overflow, underflow, bitflip or what have you all can > > fail the fast path. > > > > Once that happens and the kernel crashes with a null pointer deref, > > here is a crash at netgate which prodded this: > > calltrap() at calltrap+0x8/frame 0xfffffe0106720920 > > --- trap 0xc, rip =3D 0xffffffff80d5ab70, rsp =3D 0xfffffe01067209f0, r= bp > > =3D 0xfffffe0106720a00 --- > > turnstile_broadcast() at turnstile_broadcast+0x40/frame 0xfffffe0106720= a00 > > __rw_wunlock_hard() at __rw_wunlock_hard+0x9e/frame 0xfffffe0106720a30 > > nd6_resolve_slow() at nd6_resolve_slow+0x2d7/frame 0xfffffe0106720aa0 > > nd6_resolve() at nd6_resolve+0x125/frame 0xfffffe0106720b10 > > ether_output() at ether_output+0x4e7/frame 0xfffffe0106720ba0 > > ip_output_send() at ip_output_send+0xdc/frame 0xfffffe0106720be0 > > ip_output() at ip_output+0x1295/frame 0xfffffe0106720ce0 > > ip_forward() at ip_forward+0x3c2/frame 0xfffffe0106720d90 > > ip_input() at ip_input+0x705/frame 0xfffffe0106720df0 > > swi_net() at swi_net+0x138/frame 0xfffffe0106720e60 > > ithread_loop() at ithread_loop+0x257/frame 0xfffffe0106720ef0 > > fork_exit() at fork_exit+0x7f/frame 0xfffffe0106720f30 > > fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe0106720f30 > > --- trap 0, rip =3D 0, rsp =3D 0, rbp =3D 0 --- > > > > Neither the register dump nor anything in the backtrace indicate what h= appened. > > > > Since the kernel is going down anyway, one may as well get some debug f= rom it. > > If you don't mind the extra branches for sanity checks, why not just run = with > INVARIANTS? That is, what makes these particular assertions different fr= om > other assertions such that they should be on unconditionally? The last l= ine below > applies to pretty much every other assertion in the tree. > This adds a branch in the slowpath, a spot which should relatively rarely execute compared to the fast path. On top of that the branch at hand does not do any extra memory accesses or complex arithmetic. So no, I don't think I may as well run with INVARIANTS. --=20 Mateusz Guzik