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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 31 Oct 2018 17:33:50 -0000 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22036.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w9VHXnIF33095830 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 31 Oct 2018 17:33:49 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 558FAB2066; Wed, 31 Oct 2018 17:33:49 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 239AAB206E; Wed, 31 Oct 2018 17:33:49 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.141]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Wed, 31 Oct 2018 17:33:49 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id CFDB116C0BB2; Wed, 31 Oct 2018 10:33:49 -0700 (PDT) Date: Wed, 31 Oct 2018 10:33:49 -0700 From: "Paul E. McKenney" To: Oleg Nesterov Cc: peterz@infradead.org, linux-kernel@vger.kernel.org, josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com Subject: Re: [PATCH RFC kenrel/rcu] Eliminate BUG_ON() for sync.c Reply-To: paulmck@linux.ibm.com References: <20181022145241.GA7488@linux.ibm.com> <20181022152406.GA7257@redhat.com> <20181022155644.GG4170@linux.ibm.com> <20181022161439.GA8640@redhat.com> <20181030175539.GL4170@linux.ibm.com> <20181031172604.GC21207@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181031172604.GC21207@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18103117-0068-0000-0000-00000357301F X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009960; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000268; SDB=6.01110710; UDB=6.00575542; IPR=6.00890802; MB=3.00023981; MTD=3.00000008; XFM=3.00000015; UTC=2018-10-31 17:33:52 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18103117-0069-0000-0000-00004644AA0B Message-Id: <20181031173349.GF4170@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-10-31_06:,, 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=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1810310146 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 31, 2018 at 06:26:05PM +0100, Oleg Nesterov wrote: > On 10/30, Paul E. McKenney wrote: > > > > On Mon, Oct 22, 2018 at 06:14:40PM +0200, Oleg Nesterov wrote: > > > > > ---------------------------------------------------------------------------- > > > > > Damn. > > > > > > > > > > This suddenly reminds me that I rewrote this code completely, and you even > > > > > reviewed the new implementation and (iirc) acked it! > > > > > > > > > > However, I failed to force myself to rewrite the comments, and that is why > > > > > I didn't send the "official" patch :/ > > > > > > > > > > May be some time... > > > > > > > > Could you please point me at the last email thread? Yes, I should be > > > > able to find it, but I would probably get the wrong one. :-/ > > > > > > probably this one, > > > > > > [PATCH] rcu_sync: simplify the state machine, introduce __rcu_sync_enter() > > > https://lkml.org/lkml/2016/7/16/150 > > > > > > but I am not sure, will recheck tomorrow. > > > > Just following up... Here is what I currently have. > > Hmm. Are you sure you replied to the correct message? ;) > > the patch below looks absolutely unrelated... Oy... Right message, wrong commit. Does the one below look somewhat more relevant? ;-) Thanx, Paul ------------------------------------------------------------------------ commit 10314fde6fcdbaaf7c21b539dd2db5933344344f Author: Paul E. McKenney Date: Mon Oct 22 07:43:22 2018 -0700 rcu: Eliminate BUG_ON() for sync.c The sync.c file has a number of calls to BUG_ON(), which panics the kernel, which is not a good strategy for devices (like embedded) that don't have a way to capture console output. This commit therefore changes these BUG_ON() calls to WARN_ON_ONCE(), but does so quite naively. Reported-by: Linus Torvalds Signed-off-by: Paul E. McKenney Cc: Oleg Nesterov Cc: Peter Zijlstra diff --git a/kernel/rcu/sync.c b/kernel/rcu/sync.c index 3f943efcf61c..a6ba446a9693 100644 --- a/kernel/rcu/sync.c +++ b/kernel/rcu/sync.c @@ -125,8 +125,7 @@ void rcu_sync_enter(struct rcu_sync *rsp) rsp->gp_state = GP_PENDING; spin_unlock_irq(&rsp->rss_lock); - BUG_ON(need_wait && need_sync); - + WARN_ON_ONCE(need_wait && need_sync); if (need_sync) { gp_ops[rsp->gp_type].sync(); rsp->gp_state = GP_PASSED; @@ -139,7 +138,7 @@ void rcu_sync_enter(struct rcu_sync *rsp) * Nobody has yet been allowed the 'fast' path and thus we can * avoid doing any sync(). The callback will get 'dropped'. */ - BUG_ON(rsp->gp_state != GP_PASSED); + WARN_ON_ONCE(rsp->gp_state != GP_PASSED); } } @@ -166,8 +165,8 @@ static void rcu_sync_func(struct rcu_head *rhp) struct rcu_sync *rsp = container_of(rhp, struct rcu_sync, cb_head); unsigned long flags; - BUG_ON(rsp->gp_state != GP_PASSED); - BUG_ON(rsp->cb_state == CB_IDLE); + WARN_ON_ONCE(rsp->gp_state != GP_PASSED); + WARN_ON_ONCE(rsp->cb_state == CB_IDLE); spin_lock_irqsave(&rsp->rss_lock, flags); if (rsp->gp_count) { @@ -225,7 +224,7 @@ void rcu_sync_dtor(struct rcu_sync *rsp) { int cb_state; - BUG_ON(rsp->gp_count); + WARN_ON_ONCE(rsp->gp_count); spin_lock_irq(&rsp->rss_lock); if (rsp->cb_state == CB_REPLAY) @@ -235,6 +234,6 @@ void rcu_sync_dtor(struct rcu_sync *rsp) if (cb_state != CB_IDLE) { gp_ops[rsp->gp_type].wait(); - BUG_ON(rsp->cb_state != CB_IDLE); + WARN_ON_ONCE(rsp->cb_state != CB_IDLE); } }