From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752581AbdHJKeM (ORCPT ); Thu, 10 Aug 2017 06:34:12 -0400 Received: from LGEAMRELO11.lge.com ([156.147.23.51]:43300 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752261AbdHJKeK (ORCPT ); Thu, 10 Aug 2017 06:34:10 -0400 X-Original-SENDERIP: 156.147.1.121 X-Original-MAILFROM: byungchul.park@lge.com X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com Date: Thu, 10 Aug 2017 19:32:53 +0900 From: Byungchul Park To: Peter Zijlstra Cc: mingo@kernel.org, tglx@linutronix.de, walken@google.com, boqun.feng@gmail.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: <20170810103253.GB20323@X58A-UD3R> References: <1502089981-21272-1-git-send-email-byungchul.park@lge.com> <1502089981-21272-7-git-send-email-byungchul.park@lge.com> <20170809141605.7r3cldc4na3skcnp@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170809141605.7r3cldc4na3skcnp@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 09, 2017 at 04:16:05PM +0200, Peter Zijlstra wrote: > > Hehe, _another_ scheme... > > Yes I think this works.. but I had just sort of understood the last one. > > How about I do this on top? That I think is a combination of what I > proposed last and your single invalidate thing. Combined they solve the > problem with the least amount of extra storage (a single int). > I like your trying because it looks like making code simple, but there are some cases the patch does not cover. pppppppppppppppwwwwwwwwwwwwwwwwwwwwwwwwwiiiiiiiiiiiii wrapped > iiiiiiiiiiiiiiiiiiiii................................ where, p: process w: work i: irq In this case, your patch cannot detect overwriting 'w' with 'i'. What do you think about it? > --- > Subject: lockdep: Simplify xhlock ring buffer invalidation > From: Peter Zijlstra > Date: Wed Aug 9 15:31:27 CEST 2017 > > > Signed-off-by: Peter Zijlstra (Intel) > --- > include/linux/lockdep.h | 20 ----------- > include/linux/sched.h | 4 -- > kernel/locking/lockdep.c | 82 ++++++++++++++++++++++++++++++----------------- > 3 files changed, 54 insertions(+), 52 deletions(-) > > --- a/include/linux/lockdep.h > +++ b/include/linux/lockdep.h > @@ -284,26 +284,6 @@ struct held_lock { > */ > struct hist_lock { > /* > - * Id for each entry in the ring buffer. This is used to > - * decide whether the ring buffer was overwritten or not. > - * > - * For example, > - * > - * |<----------- hist_lock ring buffer size ------->| > - * pppppppppppppppppppppiiiiiiiiiiiiiiiiiiiiiiiiiiiii > - * wrapped > iiiiiiiiiiiiiiiiiiiiiiiiiii....................... > - * > - * where 'p' represents an acquisition in process > - * context, 'i' represents an acquisition in irq > - * context. > - * > - * In this example, the ring buffer was overwritten by > - * acquisitions in irq context, that should be detected on > - * rollback or commit. > - */ > - unsigned int hist_id; > - > - /* > * Seperate stack_trace data. This will be used at commit step. > */ > struct stack_trace trace; > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -855,9 +855,7 @@ 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]; > + unsigned int xhlock_idx_max; > #endif > > #ifdef CONFIG_UBSAN > --- a/kernel/locking/lockdep.c > +++ b/kernel/locking/lockdep.c > @@ -4818,26 +4818,65 @@ void crossrelease_hist_start(enum contex > { > 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 context_t c) > { > struct task_struct *cur = current; > + unsigned int idx; > > - if (cur->xhlocks) { > - unsigned int idx = cur->xhlock_idx_hist[c]; > - struct hist_lock *h = &xhlock(idx); > - > - cur->xhlock_idx = idx; > - > - /* Check if the ring was overwritten. */ > - if (h->hist_id != cur->hist_id_save[c]) > - invalidate_xhlock(h); > - } > + if (!cur->xhlocks) > + return; > + > + idx = cur->xhlock_idx_hist[c]; > + cur->xhlock_idx = idx; > + > + /* > + * A bit of magic here.. this deals with rewinding the (cyclic) history > + * array further than its size. IOW. looses the complete history. > + * > + * We detect this by tracking the previous oldest entry we've (over) > + * written in @xhlock_idx_max, this means the next entry is the oldest > + * entry still in the buffer, ie. its tail. > + * > + * So when we restore an @xhlock_idx that is at least MAX_XHLOCKS_NR > + * older than @xhlock_idx_max we know we've just wiped the entire > + * history. > + */ > + if ((cur->xhlock_idx_max - idx) < MAX_XHLOCKS_NR) > + return; > + > + /* > + * Now that we know the buffer is effectively empty, reset our state > + * such that it appears empty (without in fact clearing the entire > + * buffer). > + * > + * Pick @idx as the 'new' beginning, (re)set all save-points to not > + * rewind past it and reset the max. Then invalidate this idx such that > + * commit_xhlocks() will never rewind past it. Since xhlock_idx_inc() > + * will return the _next_ entry, we'll not overwrite this invalid entry > + * until the entire buffer is full again. > + */ > + for (c = 0; c < XHLOCK_NR; c++) > + cur->xhlock_idx_hist[c] = idx; > + cur->xhlock_idx_max = idx; > + invalidate_xhlock(&xhlock(idx)); > +} > + > +static inline unsigned int xhlock_idx_inc(void) > +{ > + struct task_struct *cur = current; > + unsigned int idx = ++cur->xhlock_idx; > + > + /* > + * As per the requirement in crossrelease_hist_end(), track the tail. > + */ > + if ((int)(cur->xhlock_idx_max - idx) < 0) > + cur->xhlock_idx_max = idx; > + > + return idx; > } > > static int cross_lock(struct lockdep_map *lock) > @@ -4902,7 +4941,7 @@ static inline int xhlock_valid(struct hi > */ > static void add_xhlock(struct held_lock *hlock) > { > - unsigned int idx = ++current->xhlock_idx; > + unsigned int idx = xhlock_idx_inc(); > struct hist_lock *xhlock = &xhlock(idx); > > #ifdef CONFIG_DEBUG_LOCKDEP > @@ -4915,7 +4954,6 @@ static void add_xhlock(struct held_lock > > /* Initialize hist_lock's members */ > xhlock->hlock = *hlock; > - xhlock->hist_id = current->hist_id++; > > xhlock->trace.nr_entries = 0; > xhlock->trace.max_entries = MAX_XHLOCK_TRACE_ENTRIES; > @@ -5071,7 +5109,6 @@ static int commit_xhlock(struct cross_lo > 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 i; > > if (!graph_lock()) > @@ -5091,17 +5128,6 @@ static void commit_xhlocks(struct cross_ > break; > > /* > - * Filter out the cases that the ring buffer was > - * overwritten and the previous entry has a bigger > - * hist_id than the following one, which is impossible > - * otherwise. > - */ > - if (unlikely(before(xhlock->hist_id, prev_hist_id))) > - break; > - > - prev_hist_id = xhlock->hist_id; > - > - /* > * commit_xhlock() returns 0 with graph_lock already > * released if fail. > */ > @@ -5186,11 +5212,9 @@ void lockdep_init_task(struct task_struc > int i; > > task->xhlock_idx = UINT_MAX; > - task->hist_id = 0; > > 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,