From nobody Tue Jan 18 21:35:41 2022 X-Original-To: dev-commits-src-main@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 18348195479B; Tue, 18 Jan 2022 21:36:47 +0000 (UTC) (envelope-from vladimir@kondratyev.su) Received: from corp.infotel.ru (corp.infotel.ru [195.170.219.3]) by mx1.freebsd.org (Postfix) with ESMTP id 4JdhtQ5dblz4Tsk; Tue, 18 Jan 2022 21:36:46 +0000 (UTC) (envelope-from vladimir@kondratyev.su) Received: from corp (corp.infotel.ru [195.170.219.3]) by corp.infotel.ru (Postfix) with ESMTP id E6304308F76; Wed, 19 Jan 2022 00:36:37 +0300 (MSK) X-Virus-Scanned: amavisd-new at corp.infotel.ru Received: from corp.infotel.ru ([195.170.219.3]) by corp (corp.infotel.ru [195.170.219.3]) (amavisd-new, port 10024) with ESMTP id 0sgvjYMfIRdy; Wed, 19 Jan 2022 00:36:33 +0300 (MSK) Received: from mail.cicgroup.ru (unknown [195.170.219.74]) by corp.infotel.ru (Postfix) with ESMTP id 9E344308F75; Wed, 19 Jan 2022 00:36:33 +0300 (MSK) Received: from mail.cicgroup.ru (localhost [127.0.0.1]) by mail.cicgroup.ru (Postfix) with ESMTP id 3920542211F; Wed, 19 Jan 2022 00:36:32 +0300 (MSK) Received: from mail.cicgroup.ru ([127.0.0.1]) by mail.cicgroup.ru (mail.cicgroup.ru [127.0.0.1]) (amavisd-new, port 10024) with SMTP id W7s3YkSp_1Bi; Wed, 19 Jan 2022 00:36:22 +0300 (MSK) Received: from [127.0.0.1] (localhost [127.0.0.1]) by mail.cicgroup.ru (Postfix) with ESMTPA id D229642211C; Wed, 19 Jan 2022 00:36:22 +0300 (MSK) Message-ID: <540a6a93-3101-02e8-b86a-50caa19f9653@kondratyev.su> Date: Wed, 19 Jan 2022 00:35:41 +0300 List-Id: Commit messages for the main branch of the src repository List-Archive: https://lists.freebsd.org/archives/dev-commits-src-main List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-dev-commits-src-main@freebsd.org X-BeenThere: dev-commits-src-main@freebsd.org MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: git: 02ea6033020e - main - LinuxKPI: Allow spin_lock_irqsave to be called within a critical section Content-Language: en-US To: Konstantin Belousov , Vladimir Kondratyev Cc: src-committers@freebsd.org, dev-commits-src-all@freebsd.org, dev-commits-src-main@freebsd.org References: <202201182015.20IKFaWL053942@gitrepo.freebsd.org> From: Vladimir Kondratyev In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 4JdhtQ5dblz4Tsk X-Spamd-Bar: ---- Authentication-Results: mx1.freebsd.org; none X-Spamd-Result: default: False [-4.00 / 15.00]; REPLY(-4.00)[] X-ThisMailContainsUnwantedMimeParts: N On 18.01.2022 23:22, Konstantin Belousov wrote: > On Tue, Jan 18, 2022 at 08:15:36PM +0000, Vladimir Kondratyev wrote: >> The branch main has been updated by wulf: >> >> URL: https://cgit.FreeBSD.org/src/commit/?id=02ea6033020e11afec6472bf560b0ddebd0fa97a >> >> commit 02ea6033020e11afec6472bf560b0ddebd0fa97a >> Author: Vladimir Kondratyev >> AuthorDate: 2022-01-18 20:14:12 +0000 >> Commit: Vladimir Kondratyev >> CommitDate: 2022-01-18 20:14:12 +0000 >> >> LinuxKPI: Allow spin_lock_irqsave to be called within a critical section >> >> with spinning on spin_trylock. dma-buf part of drm-kmod depends on this >> property and absence of it support results in "mi_switch: switch in a >> critical section" assertions [1][2]. >> >> [1] https://github.com/freebsd/drm-kmod/issues/116 >> [2] https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=261166 >> >> MFC after: 1 week >> Reviewed by: manu >> Differential Revision: https://reviews.freebsd.org/D33887 >> --- >> .../linuxkpi/common/include/linux/spinlock.h | 27 ++++++++++++++++++---- >> 1 file changed, 23 insertions(+), 4 deletions(-) >> >> diff --git a/sys/compat/linuxkpi/common/include/linux/spinlock.h b/sys/compat/linuxkpi/common/include/linux/spinlock.h >> index a87cb7180b28..31d47fa73986 100644 >> --- a/sys/compat/linuxkpi/common/include/linux/spinlock.h >> +++ b/sys/compat/linuxkpi/common/include/linux/spinlock.h >> @@ -37,6 +37,7 @@ >> #include >> #include >> #include >> +#include >> >> #include >> #include >> @@ -117,14 +118,32 @@ typedef struct { >> local_bh_disable(); \ >> } while (0) >> >> -#define spin_lock_irqsave(_l, flags) do { \ >> - (flags) = 0; \ >> - spin_lock(_l); \ >> +#define __spin_trylock_nested(_l, _n) ({ \ >> + int __ret; \ >> + if (SPIN_SKIP()) { \ >> + __ret = 1; \ >> + } else { \ >> + __ret = mtx_trylock_flags(&(_l)->m, MTX_DUPOK); \ >> + if (likely(__ret != 0)) \ >> + local_bh_disable(); \ >> + } \ >> + __ret; \ >> +}) >> + >> +#define spin_lock_irqsave(_l, flags) do { \ >> + (flags) = 0; \ >> + if (unlikely(curthread->td_critnest != 0)) \ >> + while (!spin_trylock(_l)) {} \ >> + else \ >> + spin_lock(_l); \ >> } while (0) >> >> #define spin_lock_irqsave_nested(_l, flags, _n) do { \ >> (flags) = 0; \ >> - spin_lock_nested(_l, _n); \ >> + if (unlikely(curthread->td_critnest != 0)) \ >> + while (!__spin_trylock_nested(_l, _n)) {} \ >> + else \ >> + spin_lock_nested(_l, _n); \ >> } while (0) >> >> #define spin_unlock_irqrestore(_l, flags) do { \ > You are spin-waiting for blockable mutex, am I right? Both, yes and no. On Linux spin_lock_irqsave is generally unblockable as it disables preemption and interrupts while our version does not do this as LinuxKPI is not ready for such a tricks. It seems that we should explicitly add critical_enter()/critical_exit calls to related dma-buf parts to make it unblockable too. This means a deadlock. > Just for example, on UP machine the spinning thread could starve the thread > that owns the mutex, which never gets to the CPU. Any ideas how to avoid it in a generic way? -- WBR Vladimir Kondratyev