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bh=4LaucvtloWCHpaXc2axnPFcfthuhw0RH1IRv8sUy6fI=; b=Az2OzX9RYGO8kSztwAv4FZoRnv5TOlOzw0ViMusf5VKfMCKXaADhC0TL7skKzP8DIheEch bWfai/uJzSP/rQvtcCOjTq3oQsYuJA704x2WmTkwkrMt39x3fItBjoXz1pHH9RDYLD0NOF Hxc172rmIwbv7DbuXntJ9W00Y1Slafs= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id AFF7D1390F; Tue, 11 Jul 2023 20:47:24 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id lGSQKNy/rWQOKQAAMHmgww (envelope-from ); Tue, 11 Jul 2023 20:47:24 +0000 Date: Tue, 11 Jul 2023 22:47:24 +0200 From: Michal Hocko To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, Oscar Salvador , Jonathan Corbet , Andrew Morton Subject: Re: [PATCH v1] mm/memory_hotplug: document the signal_pending() check in offline_pages() Message-ID: References: <20230711174050.603820-1-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230711174050.603820-1-david@redhat.com> X-Rspamd-Queue-Id: 91E8714000C X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: ir7y1amf5dgpgbgnue8zqgckuj7d7yfx X-HE-Tag: 1689108446-275406 X-HE-Meta: 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 /YEnpUne JBFO6Na5fUp+YUr781xnYBO36liyukme1F6l+raLNWe3OgkPAQ3qsNGY2ufyIBdgspdpEHgDgAA0V4zuwirXVfHmuJJEFLy/Mng84wpPOyltrXJa+AwnLCH38T7ZNpIiiLwMKmgpSNHLfto9zjEcqW2+2OdVvuK0vJQJZf7SVlqGvS9alNOFYKbKu34WoMS9h1a2iYCuZVW39LkovuhWNRT3y57MPbaM4LIM3DQrrdVWZ6NkPMVP+IIpCLX37JJG8pk8HNiZrEU5u9pESfnHloHLpwu8G6kDE2Vt2InXn2gMOVgWgfvSZ32SjOGJscUMLXwnX7Laar3RGg8JC7PHoPxRJxs8Vt+GZwXb2kXxF1lA0lJ4bSXOqsb2PgKtJnLviRv3h X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue 11-07-23 19:40:50, David Hildenbrand wrote: > Let's update the documentation that any signal is sufficient, and > add a comment that not only checking for fatal signals is historical > baggage: changing it now could break existing user space. although > unlikely. > > For example, when an app provides a custom SIGALRM handler and triggers > memory offlining, the timeout cmd would no longer stop memory offlining, > because SIGALRM would no longer be considered a fatal signal. Yes, and it is likely goot to mention here that this is an antipattern for many other kernel operations like IO (e.g. write) but it is a long term behavior that somebody might depend on and it is safer to reflect the documentation to the realitity rather than other way around (which would be imho better). > Cc: Michal Hocko > Cc: Oscar Salvador > Cc: Jonathan Corbet > Cc: Andrew Morton > Signed-off-by: David Hildenbrand Acked-by: Michal Hocko > --- > Documentation/admin-guide/mm/memory-hotplug.rst | 2 +- > mm/memory_hotplug.c | 5 +++++ > 2 files changed, 6 insertions(+), 1 deletion(-) > > diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst > index 1b02fe5807cc..bd77841041af 100644 > --- a/Documentation/admin-guide/mm/memory-hotplug.rst > +++ b/Documentation/admin-guide/mm/memory-hotplug.rst > @@ -669,7 +669,7 @@ when still encountering permanently unmovable pages within ZONE_MOVABLE > (-> BUG), memory offlining will keep retrying until it eventually succeeds. > > When offlining is triggered from user space, the offlining context can be > -terminated by sending a fatal signal. A timeout based offlining can easily be > +terminated by sending a signal. A timeout based offlining can easily be > implemented via:: > > % timeout $TIMEOUT offline_block | failure_handling > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 3f231cf1b410..7cfd13c91568 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1843,6 +1843,11 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages, > do { > pfn = start_pfn; > do { > + /* > + * Historically we always checked for any signal and > + * can't limit it to fatal signals without eventually > + * breaking user space. > + */ > if (signal_pending(current)) { > ret = -EINTR; > reason = "signal backoff"; > -- > 2.41.0 -- Michal Hocko SUSE Labs