Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752469AbdHJNR0 (ORCPT ); Thu, 10 Aug 2017 09:17:26 -0400 Received: from mail-pg0-f65.google.com ([74.125.83.65]:35890 "EHLO mail-pg0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751972AbdHJNRZ (ORCPT ); Thu, 10 Aug 2017 09:17:25 -0400 Date: Thu, 10 Aug 2017 21:17:37 +0800 From: Boqun Feng To: Byungchul Park Cc: peterz@infradead.org, mingo@kernel.org, tglx@linutronix.de, walken@google.com, kirill@shutemov.name, linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, willy@infradead.org, npiggin@gmail.com, kernel-team@lge.com Subject: Re: [PATCH v8 06/14] lockdep: Detect and handle hist_lock ring buffer overwrite Message-ID: <20170810131737.skdyy4qcxlikbyeh@tardis> References: <1502089981-21272-1-git-send-email-byungchul.park@lge.com> <1502089981-21272-7-git-send-email-byungchul.park@lge.com> <20170810115922.kegrfeg6xz7mgpj4@tardis> <016b01d311d1$d02acfa0$70806ee0$@lge.com> <20170810125133.2poixhni4d5aqkpy@tardis> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170810125133.2poixhni4d5aqkpy@tardis> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by nfs id v7ADHVbZ017028 Content-Length: 4915 Lines: 153 On Thu, Aug 10, 2017 at 08:51:33PM +0800, Boqun Feng wrote: [...] > > > > + /* Check if the ring was overwritten. */ > > > > + if (h->hist_id != cur->hist_id_save[c]) > > > > > > Could we use: > > > > > > if (h->hist_id != idx) > > > > No, we cannot. > > > > Hey, I'm not buying it. task_struct::hist_id and task_struct::xhlock_idx > are increased at the same place(in add_xhlock()), right? > > And, yes, xhlock_idx will get decreased when we do ring-buffer > unwinding, but that's OK, because we need to throw away those recently > added items. > > And xhlock_idx always points to the most recently added valid item, > right? Any other item's idx must "before()" the most recently added > one's, right? So ::xhlock_idx acts just like a timestamp, doesn't it? > > Maybe I'm missing something subtle, but could you show me an example, > that could end up being a problem if we use xhlock_idx as the hist_id? > > > hist_id is a kind of timestamp and used to detect overwriting > > data into places of same indexes of the ring buffer. And idx is > > just an index. :) IOW, they mean different things. > > > > > > > > here, and > > > > > > > + invalidate_xhlock(h); > > > > + } > > > > } > > > > > > > > static int cross_lock(struct lockdep_map *lock) > > > > @@ -4826,6 +4851,7 @@ static inline int depend_after(struct held_lock > > > *hlock) > > > > * Check if the xhlock is valid, which would be false if, > > > > * > > > > * 1. Has not used after initializaion yet. > > > > + * 2. Got invalidated. > > > > * > > > > * Remind hist_lock is implemented as a ring buffer. > > > > */ > > > > @@ -4857,6 +4883,7 @@ static void add_xhlock(struct held_lock *hlock) > > > > > > > > /* Initialize hist_lock's members */ > > > > xhlock->hlock = *hlock; > > > > + xhlock->hist_id = current->hist_id++; > > Besides, is this code correct? Does this just make xhlock->hist_id > one-less-than the curr->hist_id, which cause the invalidation every time > you do ring buffer unwinding? > > Regards, > Boqun > So basically, I'm suggesting do this on top of your patch, there is also a fix in commit_xhlocks(), which I think you should swap the parameters in before(...), no matter using task_struct::hist_id or using task_struct::xhlock_idx as the timestamp. Hope this could make my point more clear, and if I do miss something, please point it out, thanks ;-) Regards, Boqun ------------>8 diff --git a/include/linux/sched.h b/include/linux/sched.h index 074872f016f8..886ba79bfc38 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -854,9 +854,6 @@ struct task_struct { unsigned int xhlock_idx; /* For restoring at history boundaries */ unsigned int xhlock_idx_hist[XHLOCK_NR]; - unsigned int hist_id; - /* For overwrite check at each context exit */ - unsigned int hist_id_save[XHLOCK_NR]; #endif #ifdef CONFIG_UBSAN diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 699fbeab1920..04c6c8d68e18 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -4752,10 +4752,8 @@ void crossrelease_hist_start(enum xhlock_context_t c) { struct task_struct *cur = current; - if (cur->xhlocks) { + if (cur->xhlocks) cur->xhlock_idx_hist[c] = cur->xhlock_idx; - cur->hist_id_save[c] = cur->hist_id; - } } void crossrelease_hist_end(enum xhlock_context_t c) @@ -4769,7 +4767,7 @@ void crossrelease_hist_end(enum xhlock_context_t c) cur->xhlock_idx = idx; /* Check if the ring was overwritten. */ - if (h->hist_id != cur->hist_id_save[c]) + if (h->hist_id != idx) invalidate_xhlock(h); } } @@ -4849,7 +4847,7 @@ static void add_xhlock(struct held_lock *hlock) /* Initialize hist_lock's members */ xhlock->hlock = *hlock; - xhlock->hist_id = current->hist_id++; + xhlock->hist_id = idx; xhlock->trace.nr_entries = 0; xhlock->trace.max_entries = MAX_XHLOCK_TRACE_ENTRIES; @@ -5005,7 +5003,7 @@ static int commit_xhlock(struct cross_lock *xlock, struct hist_lock *xhlock) static void commit_xhlocks(struct cross_lock *xlock) { unsigned int cur = current->xhlock_idx; - unsigned int prev_hist_id = xhlock(cur).hist_id; + unsigned int prev_hist_id = cur + 1; unsigned int i; if (!graph_lock()) @@ -5030,7 +5028,7 @@ static void commit_xhlocks(struct cross_lock *xlock) * hist_id than the following one, which is impossible * otherwise. */ - if (unlikely(before(xhlock->hist_id, prev_hist_id))) + if (unlikely(before(prev_hist_id, xhlock->hist_id))) break; prev_hist_id = xhlock->hist_id; @@ -5120,12 +5118,9 @@ void lockdep_init_task(struct task_struct *task) int i; task->xhlock_idx = UINT_MAX; - task->hist_id = 0; - for (i = 0; i < XHLOCK_NR; i++) { + for (i = 0; i < XHLOCK_NR; i++) task->xhlock_idx_hist[i] = UINT_MAX; - task->hist_id_save[i] = 0; - } task->xhlocks = kzalloc(sizeof(struct hist_lock) * MAX_XHLOCKS_NR, GFP_KERNEL);