From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1FC8DECAAA6 for ; Fri, 26 Aug 2022 16:51:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343731AbiHZQvQ (ORCPT ); Fri, 26 Aug 2022 12:51:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48912 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344919AbiHZQug (ORCPT ); Fri, 26 Aug 2022 12:50:36 -0400 Received: from smtp-fw-9102.amazon.com (smtp-fw-9102.amazon.com [207.171.184.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5EABBE1A81; Fri, 26 Aug 2022 09:48:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1661532534; x=1693068534; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=oNPV4BNVK8w46WC89R5F/TMeysI1ei1JoTS87dugVG4=; b=q0ABLHs/D8HGrZSrKfCNSD1SnHllNnJkXGXZrD+UVP/4Iz03V/7GULfI 2uUFC8YqHFg1tKqzePmeqE4Fxqq9x6vDQU48ON296g6U8Kmu6A94K1WQe AYWVW67e6CxBggOUQj3ttpyvTzERY4F7asJyc13NmxDGITD5feVQqpry4 M=; X-IronPort-AV: E=Sophos;i="5.93,265,1654560000"; d="scan'208";a="253268213" Received: from pdx4-co-svc-p1-lb2-vlan2.amazon.com (HELO email-inbound-relay-iad-1a-e823fbde.us-east-1.amazon.com) ([10.25.36.210]) by smtp-border-fw-9102.sea19.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Aug 2022 16:48:20 +0000 Received: from EX13MTAUWB001.ant.amazon.com (iad12-ws-svc-p26-lb9-vlan3.iad.amazon.com [10.40.163.38]) by email-inbound-relay-iad-1a-e823fbde.us-east-1.amazon.com (Postfix) with ESMTPS id 7D9E3C0292; Fri, 26 Aug 2022 16:48:16 +0000 (UTC) Received: from EX19D004ANA001.ant.amazon.com (10.37.240.138) by EX13MTAUWB001.ant.amazon.com (10.43.161.207) with Microsoft SMTP Server (TLS) id 15.0.1497.38; Fri, 26 Aug 2022 16:48:13 +0000 Received: from 88665a182662.ant.amazon.com (10.43.162.158) by EX19D004ANA001.ant.amazon.com (10.37.240.138) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.1118.12; Fri, 26 Aug 2022 16:48:10 +0000 From: Kuniyuki Iwashima To: CC: , , , , , , , , , , , Subject: Re: [PATCH v1 net-next 01/13] fs/lock: Revive LOCK_MAND. Date: Fri, 26 Aug 2022 09:48:02 -0700 Message-ID: <20220826164802.95813-1-kuniyu@amazon.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <9312834e427a551479e1ad138b5085edaa395cdd.camel@kernel.org> References: <9312834e427a551479e1ad138b5085edaa395cdd.camel@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-Originating-IP: [10.43.162.158] X-ClientProxiedBy: EX13D43UWA004.ant.amazon.com (10.43.160.108) To EX19D004ANA001.ant.amazon.com (10.37.240.138) Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Jeff Layton Date: Fri, 26 Aug 2022 06:02:44 -0400 > On Thu, 2022-08-25 at 17:04 -0700, Kuniyuki Iwashima wrote: > > The commit 90f7d7a0d0d6 ("locks: remove LOCK_MAND flock lock support") > > removed LOCK_MAND support from the kernel because nothing checked the > > flag, nor was there no use case. This patch revives LOCK_MAND to > > introduce a mandatory lock for read/write on /proc/sys. Currently, it's > > the only use case, so we added two changes while reverting the commit. > > > > First, we used to allow any f_mode for LOCK_MAND, but now we don't get > > it back. Instead, we enforce being FMODE_READ|FMODE_WRITE as LOCK_SH > > and LOCK_EX. > > > > Second, when f_ops->flock() was called with LOCK_MAND, each function > > returned -EOPNOTSUPP. The following patch does not use f_ops->flock(), > > so we put the validation before calling f_ops->flock(). > > > > Signed-off-by: Kuniyuki Iwashima > > --- > > fs/locks.c | 57 ++++++++++++++++++++------------ > > include/uapi/asm-generic/fcntl.h | 5 --- > > 2 files changed, 35 insertions(+), 27 deletions(-) > > > > diff --git a/fs/locks.c b/fs/locks.c > > index c266cfdc3291..03ff10a3165e 100644 > > --- a/fs/locks.c > > +++ b/fs/locks.c > > @@ -421,6 +421,10 @@ static inline int flock_translate_cmd(int cmd) { > > case LOCK_UN: > > return F_UNLCK; > > } > > + > > + if (cmd & LOCK_MAND) > > + return cmd & (LOCK_MAND | LOCK_RW); > > + > > return -EINVAL; > > } > > > > @@ -879,6 +883,10 @@ static bool flock_locks_conflict(struct file_lock *caller_fl, > > if (caller_fl->fl_file == sys_fl->fl_file) > > return false; > > > > + if (caller_fl->fl_type & LOCK_MAND || > > + sys_fl->fl_type & LOCK_MAND) > > + return true; > > + > > return locks_conflict(caller_fl, sys_fl); > > } > > > > @@ -2077,9 +2085,7 @@ EXPORT_SYMBOL(locks_lock_inode_wait); > > * - %LOCK_SH -- a shared lock. > > * - %LOCK_EX -- an exclusive lock. > > * - %LOCK_UN -- remove an existing lock. > > - * - %LOCK_MAND -- a 'mandatory' flock. (DEPRECATED) > > - * > > - * %LOCK_MAND support has been removed from the kernel. > > + * - %LOCK_MAND -- a 'mandatory' flock. (only supported on /proc/sys/) > > */ > > SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd) > > { > > @@ -2087,19 +2093,6 @@ SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd) > > struct file_lock fl; > > struct fd f; > > > > - /* > > - * LOCK_MAND locks were broken for a long time in that they never > > - * conflicted with one another and didn't prevent any sort of open, > > - * read or write activity. > > - * > > - * Just ignore these requests now, to preserve legacy behavior, but > > - * throw a warning to let people know that they don't actually work. > > - */ > > - if (cmd & LOCK_MAND) { > > - pr_warn_once("Attempt to set a LOCK_MAND lock via flock(2). This support has been removed and the request ignored.\n"); > > - return 0; > > - } > > - > > type = flock_translate_cmd(cmd & ~LOCK_NB); > > if (type < 0) > > return type; > > @@ -2109,6 +2102,7 @@ SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd) > > if (!f.file) > > return error; > > > > + /* LOCK_MAND supports only read/write on proc_sysctl for now */ > > if (type != F_UNLCK && !(f.file->f_mode & (FMODE_READ | FMODE_WRITE))) > > goto out_putf; > > > > @@ -2122,12 +2116,18 @@ SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd) > > if (can_sleep) > > fl.fl_flags |= FL_SLEEP; > > > > - if (f.file->f_op->flock) > > + if (f.file->f_op->flock) { > > + if (cmd & LOCK_MAND) { > > + error = -EOPNOTSUPP; > > + goto out_putf; > > + } > > + > > error = f.file->f_op->flock(f.file, > > (can_sleep) ? F_SETLKW : F_SETLK, > > &fl); > > - else > > + } else { > > error = locks_lock_file_wait(f.file, &fl); > > + } > > > > out_putf: > > fdput(f); > > @@ -2711,7 +2711,11 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl, > > seq_printf(f, " %s ", > > (inode == NULL) ? "*NOINODE*" : "ADVISORY "); > > } else if (IS_FLOCK(fl)) { > > - seq_puts(f, "FLOCK ADVISORY "); > > + if (fl->fl_type & LOCK_MAND) { > > + seq_puts(f, "FLOCK MANDATORY "); > > + } else { > > + seq_puts(f, "FLOCK ADVISORY "); > > + } > > } else if (IS_LEASE(fl)) { > > if (fl->fl_flags & FL_DELEG) > > seq_puts(f, "DELEG "); > > @@ -2727,10 +2731,19 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl, > > } else { > > seq_puts(f, "UNKNOWN UNKNOWN "); > > } > > - type = IS_LEASE(fl) ? target_leasetype(fl) : fl->fl_type; > > > > - seq_printf(f, "%s ", (type == F_WRLCK) ? "WRITE" : > > - (type == F_RDLCK) ? "READ" : "UNLCK"); > > + if (fl->fl_type & LOCK_MAND) { > > + seq_printf(f, "%s ", > > + (fl->fl_type & LOCK_READ) > > + ? (fl->fl_type & LOCK_WRITE) ? "RW " : "READ " > > + : (fl->fl_type & LOCK_WRITE) ? "WRITE" : "NONE "); > > + } else { > > + type = IS_LEASE(fl) ? target_leasetype(fl) : fl->fl_type; > > + > > + seq_printf(f, "%s ", (type == F_WRLCK) ? "WRITE" : > > + (type == F_RDLCK) ? "READ" : "UNLCK"); > > + } > > + > > if (inode) { > > /* userspace relies on this representation of dev_t */ > > seq_printf(f, "%d %02x:%02x:%lu ", fl_pid, > > diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h > > index 1ecdb911add8..94fb8c6fd543 100644 > > --- a/include/uapi/asm-generic/fcntl.h > > +++ b/include/uapi/asm-generic/fcntl.h > > @@ -180,11 +180,6 @@ struct f_owner_ex { > > #define LOCK_NB 4 /* or'd with one of the above to prevent > > blocking */ > > #define LOCK_UN 8 /* remove lock */ > > - > > -/* > > - * LOCK_MAND support has been removed from the kernel. We leave the symbols > > - * here to not break legacy builds, but these should not be used in new code. > > - */ > > #define LOCK_MAND 32 /* This is a mandatory flock ... */ > > #define LOCK_READ 64 /* which allows concurrent read operations */ > > #define LOCK_WRITE 128 /* which allows concurrent write operations */ > > NACK. > > This may break legacy userland code that sets LOCK_MAND on flock calls > (e.g. old versions of samba). > > If you want to add a new mechanism that does something similar with a > new flag, then that may be possible, but please don't overload old flags > that could still be used in the field with new meanings. Exactly, that makes sense. Thanks for feedback! > If you do decide to use flock for this functionality (and I'm not sure > this is a good idea), Actually, the patch 1-2 were experimental to show all available options (flock()'s latency vs unshare()'s memory cost), and I like unshare(). If both of them were unacceptable, I would have added clone() BPF hook. But it seems unshare() works at least, I'll drop this part in the next spin. Thank you. > then I'd also like to see a clear description of > the semantics this provides. > -- > Jeff Layton