From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) by kanga.kvack.org (Postfix) with ESMTP id 4256C6B30E8 for ; Fri, 23 Nov 2018 06:06:24 -0500 (EST) Received: by mail-wm1-f69.google.com with SMTP id r11so1255726wmg.1 for ; Fri, 23 Nov 2018 03:06:24 -0800 (PST) Received: from Galois.linutronix.de (Galois.linutronix.de. [2a01:7a0:2:106d:700::1]) by mx.google.com with ESMTPS id u83si5994166wmb.83.2018.11.23.03.06.22 for (version=TLS1_2 cipher=AES128-SHA bits=128/128); Fri, 23 Nov 2018 03:06:23 -0800 (PST) Date: Fri, 23 Nov 2018 12:06:11 +0100 From: Sebastian Andrzej Siewior Subject: Re: [PATCH v2] kmemleak: Turn kmemleak_lock to raw spinlock on RT Message-ID: <20181123110611.s2gmd237j7docrxt@linutronix.de> References: <1542877459-144382-1-git-send-email-zhe.he@windriver.com> <20181123095314.hervxkxtqoixovro@linutronix.de> <20181123110226.GA5125@andrea> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20181123110226.GA5125@andrea> Sender: owner-linux-mm@kvack.org List-ID: To: Andrea Parri , Peter Zijlstra Cc: zhe.he@windriver.com, catalin.marinas@arm.com, tglx@linutronix.de, rostedt@goodmis.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, boqun.feng@gmail.com On 2018-11-23 12:02:55 [+0100], Andrea Parri wrote: > > is this an RT-only problem? Because mainline should not allow read->read > > locking or read->write locking for reader-writer locks. If this only > > happens on v4.18 and not on v4.19 then something must have fixed it. > > Probably misunderstanding, but I'd say that read->read locking is "the > norm"...? > > If you don't use qrwlock, readers are also "recursive", in part., > > P0 P1 > read_lock(l) > write_lock(l) > read_lock(l) > > won't block P0 on the second read_lock(). (qrwlock somehow complicate > the analysis; IIUC, they are recursive if and only if in_interrupt().). ehm, peterz, is that true? My memory on that is that all readers will block if there is a writer pending. > Andrea Sebastian