linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Alexander Shishkin <alexander.shishkin@linux.intel.com>
To: Song Liu <songliubraving@fb.com>, linux-kernel@vger.kernel.org
Cc: kernel-team@fb.com, Song Liu <songliubraving@fb.com>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	Jiri Olsa <jolsa@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	alexander.shishkin@linux.intel.com
Subject: Re: [PATCH] perf/core: fix mlock accounting in perf_mmap()
Date: Mon, 20 Jan 2020 10:24:00 +0200	[thread overview]
Message-ID: <87blqybknz.fsf@ashishki-desk.ger.corp.intel.com> (raw)
In-Reply-To: <20200117234503.1324050-1-songliubraving@fb.com>

Song Liu <songliubraving@fb.com> writes:

> sysctl_perf_event_mlock and user->locked_vm can change value
> independently, so we can't guarantee:
>
>     user->locked_vm <= user_lock_limit

This means: if the sysctl got sufficiently decreased, so that the
existing locked_vm exceeds it, we need to deal with the overflow, right?

> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index a1f8bde19b56..89acdd1574ef 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -5920,11 +5920,31 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
>  
>  	if (user_locked > user_lock_limit) {
>  		/*
> -		 * charge locked_vm until it hits user_lock_limit;
> -		 * charge the rest from pinned_vm
> +		 * sysctl_perf_event_mlock and user->locked_vm can change
> +		 * value independently, so we can't guarantee:
> +		 *
> +		 *    user->locked_vm <= user_lock_limit
> +		 *
> +		 * We need be careful to make sure user_extra >=0.
> +		 *
> +		 * Using "user_locked - user_extra" to avoid calling
> +		 * atomic_long_read() again.
>  		 */
> -		extra = user_locked - user_lock_limit;
> -		user_extra -= extra;
> +		if (user_locked - user_extra >= user_lock_limit) {
> +			/*
> +			 * already used all user_locked_limit, charge all
> +			 * to pinned_vm
> +			 */
> +			extra = user_extra;
> +			user_extra = 0;
> +		} else {
> +			/*
> +			 * charge locked_vm until it hits user_lock_limit;
> +			 * charge the rest from pinned_vm
> +			 */
> +			extra = user_locked - user_lock_limit;
> +			user_extra -= extra;
> +		}

How about the below for the sake of brevity?

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 763cf34b5a63..632505ce6c12 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5917,7 +5917,14 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 	 */
 	user_lock_limit *= num_online_cpus();
 
-	user_locked = atomic_long_read(&user->locked_vm) + user_extra;
+	user_locked = atomic_long_read(&user->locked_vm);
+	/*
+	 * If perf_event_mlock has changed since earlier mmaps, so that
+	 * it's smaller than user->locked_vm, discard the overflow.
+	 */
+	if (user_locked > user_lock_limit)
+		user_locked = user_lock_limit;
+	user_locked += user_extra;
 
 	if (user_locked > user_lock_limit) {
 		/*

Regards,
--
Alex

  reply	other threads:[~2020-01-20  8:24 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-17 23:45 [PATCH] perf/core: fix mlock accounting in perf_mmap() Song Liu
2020-01-20  8:24 ` Alexander Shishkin [this message]
2020-01-21 18:55   ` Song Liu
2020-01-23  9:19     ` Alexander Shishkin
2020-01-23 17:24       ` Song Liu
2020-01-21 19:35   ` Song Liu
2020-01-22  8:50     ` Alexander Shishkin

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=87blqybknz.fsf@ashishki-desk.ger.corp.intel.com \
    --to=alexander.shishkin@linux.intel.com \
    --cc=acme@redhat.com \
    --cc=jolsa@kernel.org \
    --cc=kernel-team@fb.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=peterz@infradead.org \
    --cc=songliubraving@fb.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).