Date: Fri, 11 Aug 2017 09:44:54 +0900
From: Byungchul Park <byungchul.park@lge.com>
To: Boqun Feng <boqun.feng@gmail.com>
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: <20170811004453.GG20323@X58A-UD3R>
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>
 <20170810131737.skdyy4qcxlikbyeh@tardis>
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On Thu, Aug 10, 2017 at 09:17:37PM +0800, Boqun Feng wrote:
> 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 ;-)

I think I fully explained why we cannot use xhlock_idx as the timestamp
in another reply. Please let me know if it's not enough. :)

Thank you,
Byungchul

> 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);