linux-kernel - Re: [PATCH v2 09/16] rcu/tree: Maintain separate array for vmalloc ptrs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200618172504.GA14613@pc636>
Date:   Thu, 18 Jun 2020 19:25:04 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     "Uladzislau Rezki (Sony)" <urezki@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Matthew Wilcox <willy@...radead.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        RCU <rcu@...r.kernel.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: Re: [PATCH v2 09/16] rcu/tree: Maintain separate array for vmalloc
 ptrs

> > +	// Handle two first channels.
> > +	for (i = 0; i < FREE_N_CHANNELS; i++) {
> > +		for (; bkvhead[i]; bkvhead[i] = bnext) {
> > +			bnext = bkvhead[i]->next;
> > +			debug_rcu_bhead_unqueue(bkvhead[i]);
> > +
> > +			rcu_lock_acquire(&rcu_callback_map);
> > +			if (i == 0) { // kmalloc() / kfree().
> > +				trace_rcu_invoke_kfree_bulk_callback(
> > +					rcu_state.name, bkvhead[i]->nr_records,
> > +					bkvhead[i]->records);
> > +
> > +				kfree_bulk(bkvhead[i]->nr_records,
> > +					bkvhead[i]->records);
> > +			} else { // vmalloc() / vfree().
> > +				for (j = 0; j < bkvhead[i]->nr_records; j++) {
> > +					trace_rcu_invoke_kfree_callback(
> > +						rcu_state.name,
> > +						bkvhead[i]->records[j], 0);
> > +
> > +					vfree(bkvhead[i]->records[j]);
> > +				}
> > +			}
> > +			rcu_lock_release(&rcu_callback_map);
> 
> Not an emergency, but did you look into replacing this "if" statement
> with an array of pointers to functions implementing the legs of the
> "if" statement?  If nothing else, this would greatly reduced indentation.
> 
>
> I am taking this as is, but if you have not already done so, could you
> please look into this for a follow-up patch?
> 
I do not think it makes sense, because it would require to check each
pointer in the array, what can lead to many branching, i.e. "if-else"
instructions.

Paul, thank you to take it in!

--
Vlad Rezki