linux-kernel - Re: [PATCH v3 3/5] mm: madvise: implement lightweight guard page mechanism

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Message-ID: <f09086cd-c49c-4eea-adff-d626c16083de@lucifer.local>
Date: Fri, 25 Oct 2024 18:12:18 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Suren Baghdasaryan <surenb@...gle.com>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Matthew Wilcox <willy@...radead.org>, Vlastimil Babka <vbabka@...e.cz>,
        "Paul E . McKenney" <paulmck@...nel.org>, Jann Horn <jannh@...gle.com>,
        David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Muchun Song <muchun.song@...ux.dev>,
        Richard Henderson <richard.henderson@...aro.org>,
        Matt Turner <mattst88@...il.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "James E . J . Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>, Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>, Arnd Bergmann <arnd@...nel.org>,
        linux-alpha@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, linux-arch@...r.kernel.org,
        Shuah Khan <shuah@...nel.org>, Christian Brauner <brauner@...nel.org>,
        linux-kselftest@...r.kernel.org,
        Sidhartha Kumar <sidhartha.kumar@...cle.com>,
        Jeff Xu <jeffxu@...omium.org>, Christoph Hellwig <hch@...radead.org>,
        linux-api@...r.kernel.org, John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH v3 3/5] mm: madvise: implement lightweight guard page
 mechanism

On Wed, Oct 23, 2024 at 05:24:40PM +0100, Lorenzo Stoakes wrote:
> Implement a new lightweight guard page feature, that is regions of userland
> virtual memory that, when accessed, cause a fatal signal to arise.

<snip>

Hi Andrew - Could you apply the below fix-patch? I realise we must handle
fatal signals and conditional rescheduling in the vector_madvise() special
case.

Thanks!

----8<----
>From 546d7e1831c71599fc733d589e0d75f52e84826d Mon Sep 17 00:00:00 2001
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Date: Fri, 25 Oct 2024 18:05:48 +0100
Subject: [PATCH] mm: yield on fatal signal/cond_sched() in vector_madvise()

While we have to treat -ERESTARTNOINTR specially here as we are looping
through a vector of operations and can't simply restart the entire
operation, we mustn't hold up fatal signals or RT kernels.
---
 mm/madvise.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 48eba25e25fe..127aa5d86656 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1713,8 +1713,14 @@ static ssize_t vector_madvise(struct mm_struct *mm, struct iov_iter *iter,
 		 * we have already rescinded locks, it should be no problem to
 		 * simply try again.
 		 */
-		if (ret == -ERESTARTNOINTR)
+		if (ret == -ERESTARTNOINTR) {
+			if (fatal_signal_pending(current)) {
+				ret = -EINTR;
+				break;
+			}
+			cond_resched();
 			continue;
+		}
 		if (ret < 0)
 			break;
 		iov_iter_advance(iter, iter_iov_len(iter));
--
2.47.0