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McKenney" To: Sebastian Andrzej Siewior Cc: Joel Fernandes , Scott Wood , linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, Thomas Gleixner , Peter Zijlstra , Juri Lelli , Clark Williams Subject: Re: [PATCH RT v2 2/3] sched: migrate_enable: Use sleeping_lock to indicate involuntary sleep Message-ID: <20190828155028.GP26530@linux.ibm.com> Reply-To: paulmck@kernel.org References: <20190823162024.47t7br6ecfclzgkw@linutronix.de> <433936e4c720e6b81f9b297fefaa592fd8a961ad.camel@redhat.com> <20190824031014.GB2731@google.com> <20190826152523.dcjbsgyyir4zjdol@linutronix.de> <20190826162945.GE28441@linux.ibm.com> <20190827092333.jp3darw7teyyw67g@linutronix.de> <20190827155306.GF26530@linux.ibm.com> <20190828092739.46mrffvzjv6v3de5@linutronix.de> <20190828125426.GO26530@linux.ibm.com> <20190828131433.3gi4debho5zc7hgc@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190828131433.3gi4debho5zc7hgc@linutronix.de> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-28_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=764 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908280160 Sender: linux-rt-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On Wed, Aug 28, 2019 at 03:14:33PM +0200, Sebastian Andrzej Siewior wrote: > On 2019-08-28 05:54:26 [-0700], Paul E. McKenney wrote: > > On Wed, Aug 28, 2019 at 11:27:39AM +0200, Sebastian Andrzej Siewior wrote: > > > On 2019-08-27 08:53:06 [-0700], Paul E. McKenney wrote: > > > > Am I understanding this correctly? > > > > > > Everything perfect except that it is not lockdep complaining but the > > > WARN_ON_ONCE() in rcu_note_context_switch(). > > > > This one, right? > > > > WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0); > > > > Another approach would be to change that WARN_ON_ONCE(). This fix might > > be too extreme, as it would suppress other issues: > > > > WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_RT_BASE) && !preempt && t->rcu_read_lock_nesting > 0); > > > > But maybe what is happening under the covers is that preempt is being > > set when sleeping on a spinlock. Is that the case? > > I would like to keep that check and that is why we have: > > | #if defined(CONFIG_PREEMPT_RT_FULL) > | sleeping_l = t->sleeping_lock; > | #endif > | WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0 && !sleeping_l); > > in -RT and ->sleeping_lock is that counter that is incremented in > spin_lock(). And the only reason why sleeping_lock_inc() was used in the > patch was to disable _this_ warning. Very good! I would prefer an (one-line) access function to keep the number of #if uses down to dull roar, but other than that, looks good! (Yeah, I know, this is tree_preempt.h, but still...) Thanx, Paul