From nobody Wed Dec 18 18:15:45 2024 X-Original-To: freebsd-current@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 4YD21G07tkz5hgbN for ; Wed, 18 Dec 2024 18:16:02 +0000 (UTC) (envelope-from asomers@gmail.com) Received: from mail-ed1-f48.google.com (mail-ed1-f48.google.com [209.85.208.48]) (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 4YD21F0kQxz4l5t for ; Wed, 18 Dec 2024 18:16:01 +0000 (UTC) (envelope-from asomers@gmail.com) Authentication-Results: mx1.freebsd.org; dkim=none; spf=pass (mx1.freebsd.org: domain of asomers@gmail.com designates 209.85.208.48 as permitted sender) smtp.mailfrom=asomers@gmail.com; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=freebsd.org (policy=none) Received: by mail-ed1-f48.google.com with SMTP id 4fb4d7f45d1cf-5d3e8f64d5dso12354070a12.3 for ; Wed, 18 Dec 2024 10:16:01 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1734545759; x=1735150559; h=content-transfer-encoding:cc: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=vlb8clm+GUW0C4+2M33ZNNF89F5WHms+nojnrUAe4Iw=; b=VzZbJHwCfdAXYfD2lith82vJvLSZI8Enrd7zUYHegRmwVXWZ5SI3JTdpL+C0wBMi2j 2Jt1jB3rslcLWV/ZarySj3WjMrb1AyWoGrBud6exF/nzVtgR6Wc3SZS7t5g2o9cgRJgo 0vPEDNQhkvCLEJZHoqkxWLOolQ9lorqG/zJ7z5Z2Bn06v4OjGFU0u63xpQjrQGC90jtA hjZFSsCGiZU1vo0eutBki8pMK9I2V+Y9lLZSa8Vp3iMhZ0gzjvACbHIbaNtvHV2xj9v8 EAK090IS9cx1LcQUZsi2IoCvsyD9ePygQ0dmCc68agj5mIJ4QSfgWVxlLQEkB5pFrRIA Rv+w== X-Forwarded-Encrypted: i=1; AJvYcCVFCNsvfWIpun9Bj+TNAgcWrsVBLVUAaOLvNXwsDLoyupHQMp9VIUoEDEy9HSkjG4tpgI90lSwcaOj4c+2IqGg=@freebsd.org X-Gm-Message-State: AOJu0Yxnt63PQawOtnmFe/cmB0nxi+NrOEut+nmSuyY8y0OF9MiUMvN3 C2pZyd+iyibFEb21x5h+g4mZUmleVQvTXOrjzPW755/4vBbxQKQSwXGzJVbJBuxAT4we5+hK+Ii S4eXjfW0QEiE0sX+lptel8GTMYNSNsJkH X-Gm-Gg: ASbGncuAA2TVnW6ytCqbDpstVB8KKM33E8cJa8q5ezRpu8QgQ2fCz3rbKymAmUMXLtK x/z8aEpjXuxuHWgbB1FR6l3L+iNKWlxULw/yVOg== X-Received: by 2002:a05:6402:26ca:b0:5d4:4143:c07a with SMTP id 4fb4d7f45d1cf-5d7ee3a27eemt3228143a12.1.1734545757590; Wed, 18 Dec 2024 10:15:57 -0800 (PST) List-Id: Discussions about the use of FreeBSD-current List-Archive: https://lists.freebsd.org/archives/freebsd-current List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-current@FreeBSD.org MIME-Version: 1.0 References: In-Reply-To: From: Alan Somers Date: Wed, 18 Dec 2024 11:15:45 -0700 Message-ID: Subject: Re: Why does namei return an exclusively locked vnode when LOCKSHARED is specified? Cc: Mark Johnston , FreeBSD CURRENT Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Spamd-Result: default: False [0.44 / 15.00]; MISSING_TO(2.00)[]; SUBJECT_ENDS_QUESTION(1.00)[]; NEURAL_HAM_MEDIUM(-1.00)[-0.999]; NEURAL_HAM_SHORT(-0.99)[-0.995]; NEURAL_HAM_LONG(-0.66)[-0.664]; FORGED_SENDER(0.30)[asomers@freebsd.org,asomers@gmail.com]; R_SPF_ALLOW(-0.20)[+ip4:209.85.128.0/17:c]; DMARC_POLICY_SOFTFAIL(0.10)[freebsd.org : SPF not aligned (relaxed), No valid DKIM,none]; MIME_GOOD(-0.10)[text/plain]; RCVD_TLS_LAST(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_TWO(0.00)[2]; ARC_NA(0.00)[]; TO_DN_ALL(0.00)[]; MIME_TRACE(0.00)[0:+]; MISSING_XM_UA(0.00)[]; FREEFALL_USER(0.00)[asomers]; FREEMAIL_ENVFROM(0.00)[gmail.com]; PREVIOUSLY_DELIVERED(0.00)[freebsd-current@freebsd.org]; TO_MATCH_ENVRCPT_SOME(0.00)[]; FROM_NEQ_ENVFROM(0.00)[asomers@freebsd.org,asomers@gmail.com]; RCVD_COUNT_ONE(0.00)[1]; MLMMJ_DEST(0.00)[freebsd-current@freebsd.org]; RWL_MAILSPIKE_POSSIBLE(0.00)[209.85.208.48:from]; R_DKIM_NA(0.00)[]; ASN(0.00)[asn:15169, ipnet:209.85.128.0/17, country:US]; RCVD_IN_DNSWL_NONE(0.00)[209.85.208.48:from] X-Rspamd-Queue-Id: 4YD21F0kQxz4l5t X-Spamd-Bar: / On Tue, Dec 17, 2024 at 1:02=E2=80=AFPM Alan Somers w= rote: > > On Tue, Dec 17, 2024 at 12:27=E2=80=AFPM Mark Johnston wrote: > > > > On Tue, Dec 17, 2024 at 12:19:26PM -0700, Alan Somers wrote: > > > According to namei(9), namei should return a shared lock when > > > LOCKSHARED is specified. But in my experiments, it always seems to > > > return an exclusive lock instead. For example: > > > > > > $ cd /usr/tests/sys/fs/fusefs > > > $ sudo dtrace -i 'fbt:fusefs:fuse_vnop_getattr:entry /pid=3D=3D$targe= t/ > > > {printf("islocked=3D%#x", args[0]->a_vp->v_vnlock->lk_lock); stack();= }' > > > -i 'fbt:kernel:vop_stdstat:entry /pid=3D=3D$target/ > > > {printf("islocked=3D%#x", args[0]->a_vp->v_vnlock->lk_lock);}' -c > > > "./getattr --gtest_filter=3DGetattr.attr_cache -v" > > > [=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D] Running 1 test from 1 test suite. > > > [----------] Global test environment set-up. > > > [----------] 1 test from Getattr > > > [ RUN ] Getattr.attr_cache > > > INIT ino=3D 0 > > > ACCESS ino=3D 1 mask=3D0x1 > > > LOOKUP ino=3D 1 some_file.txt > > > GETATTR ino=3D42 > > > [ OK ] Getattr.attr_cache (3 ms) > > > [----------] 1 test from Getattr (3 ms total) > > > > > > [----------] Global test environment tear-down > > > [=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D] 1 test from 1 test suite ran. (4 ms = total) > > > [ PASSED ] 1 test. > > > CPU ID FUNCTION:NAME > > > 3 19743 vop_stdstat:entry islocked=3D0x21 > > > 3 19743 vop_stdstat:entry islocked=3D0xfffff80004f1= 6740 > > > 3 68298 fuse_vnop_getattr:entry islocked=3D0xfffff80004f1= 6740 > > > kernel`VOP_GETATTR_APV+0x90 > > > kernel`vop_stdstat+0x147 > > > kernel`VOP_STAT_APV+0x91 > > > kernel`kern_statat+0x183 > > > kernel`sys_fstatat+0x27 > > > kernel`amd64_syscall+0x1af > > > kernel`0xffffffff8106cd5b > > > > > > 3 19743 vop_stdstat:entry islocked=3D0xfffff80004f1= 6740 > > > 3 68298 fuse_vnop_getattr:entry islocked=3D0xfffff80004f1= 6740 > > > kernel`VOP_GETATTR_APV+0x90 > > > kernel`vop_stdstat+0x147 > > > kernel`VOP_STAT_APV+0x91 > > > kernel`kern_statat+0x183 > > > kernel`sys_fstatat+0x27 > > > kernel`amd64_syscall+0x1af > > > kernel`0xffffffff8106cd5b > > > > > > dtrace: pid 3554 has exited > > > > > > From that output, the first vop_stdstat is probably for the > > > mountpoint, and isn't what I'm concerned about. But the second two > > > are for a fusefs file. The LK_SHARE bit is not set, indicating an > > > exclusive lock. That's even though the call to namei in kern_statat > > > specifies LOCKSHARED | LOCKLEAF. > > > > > > What am I missing? > > > > Having noticed the same phenomenon in p9fs and scratching my head for a > > while: is fusefs failing to call VN_LOCK_ASHARE() in this case? I see > > that it's predicated on "data->dataflags & FSESS_ASYNC_READ", but I'm > > not sure why - the comment seems to suggest a misunderstanding of what > > VN_LOCK_ASHARE() does. > > > > ... oh, also perhaps because fusefs mounts don't set MNTK_LOOKUP_SHARED= ? > > Yes, that's it! Both of those things need to change. Now I can get > on with solving my real bug. Thank you. FYI: this is the bug I was working on: https://github.com/freebsd/freebsd-src/pull/1556