From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 051E91DDC3F; Fri, 3 Jul 2026 09:32:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783071179; cv=none; b=n82qoQA3RKI1UCtIjE79IVXtQBveef0igLQWjvQcKw9aWoyD1K/0r1uDjhjSY+x9bd6pvMJoRPFE6Sz9LiI2fUEaLDiNN0+NvvAsI5DUrCicNcTV9sQ/G+2ApdXdNKKZVtVH7UlhgPeC+L98jl8i+253Iloy3DubHwsC4t4Iosg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783071179; c=relaxed/simple; bh=F+IExRK8dklW73F9jdhQWGmsMjAg5ll+7BDnf4TitHc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=tX60UW8Rx+z7CE9NJZ+WpkVIa8r/xeBWAulU6QhePt1j317vlGlqt3IMxBFpu2TOSEnN/bR6t+MRQAIIVLeVjBAHk1pc+ovF2ncchex6ASdYkQyAFkt1UqKZl3Nb0ERR72Wm+hs/cZqd4OO8PRs9xxnsXQEwFZmVrSJekrrSzDI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ewYhOz+y; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ewYhOz+y" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1E1451F000E9; Fri, 3 Jul 2026 09:32:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783071174; bh=e1pQpUBYSThfjFqXpi3CJbvoH2B8jgJGjXQchqDbIYs=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ewYhOz+y/2ODJQiSe/1wYQEvPysmor5pP4hs4s16yHMRJct21kwF7eTWcwUsHq5jr xbKpyswZ71LI/axa/e7vJAaK0uyh+cN3GPhs4nDzG/9z77a4NzlfWMCzpiauiYyC0G otHE19G5VpTD58+dIcVh4xBBtQWZtj8UwN7J7hGJzkPc2cNMWok0Uxe6GXgGX/iaD0 K3rlzEMJQfO8x7gTe1qKW2vhOk3n7DxihnDmtl3zT1cBAZ4JVjdKyaU0sRMvsJSUnB xUDixob2C4kwpPJB6mdECWk7woRCVBU5gPDlX7xWq0KJFCmSgxI0fipNd6D+r8yfKu yuDeJKhf3eneQ== Message-ID: <1e162a97-1594-495d-b48e-7dafaa0a6d82@kernel.org> Date: Fri, 3 Jul 2026 11:32:46 +0200 Precedence: bulk X-Mailing-List: linux-rt-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 18/18] mm: factor out can_spin_trylock() Content-Language: en-US To: Brendan Jackman , Andrew Morton , Suren Baghdasaryan , Michal Hocko , Johannes Weiner , Zi Yan , Muchun Song , Oscar Salvador , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Ying Huang , Alistair Popple , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt Cc: "Harry Yoo (Oracle)" , Gregory Price , Alexei Starovoitov , Matthew Wilcox , Hao Ge , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, derkling@google.com, reijiw@google.com, Yosry Ahmed References: <20260702-alloc-trylock-v4-0-0af8ff387e80@google.com> <20260702-alloc-trylock-v4-18-0af8ff387e80@google.com> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: <20260702-alloc-trylock-v4-18-0af8ff387e80@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/2/26 11:49, Brendan Jackman wrote: > Deduplicate checks for whether the current context is safe for > spin_trylock(). > > Does this function really belong in mm/internal.h or is it generic? Not > sure. If someone ends up duplicating this logic elsewhere in the kernel, > that would be a shame. But goes in some generic header, someone treats > it as documentation about where it's guaranteed safe to spin_trylock(), > and then it emerges that there are other subtle preconditions that > didn't affect the mm usecase, that would be worse. So, just be > conservative and keep it local. Agreed. We could even use page_alloc.h ? > Suggested-by: Harry Yoo > Link: https://lore.kernel.org/all/397859cb-b127-4cc6-9c71-044afc99bf0c@kernel.org/ > Signed-off-by: Brendan Jackman Reviewed-by: Vlastimil Babka (SUSE) > --- > mm/internal.h | 23 +++++++++++++++++++++++ > mm/page_alloc.c | 17 +---------------- > mm/slub.c | 10 +--------- > 3 files changed, 25 insertions(+), 25 deletions(-) > > diff --git a/mm/internal.h b/mm/internal.h > index 3c00eaf5f45a4..e6f300693ffd7 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -1715,4 +1715,27 @@ static inline void mm_prepare_for_swap_entries(struct mm_struct *mm) > } > } > > +static inline bool can_spin_trylock(void) > +{ > + /* > + * In PREEMPT_RT spin_trylock() will call raw_spin_lock() which is > + * unsafe in NMI. If spin_trylock() is called from hard IRQ the current > + * task may be waiting for one rt_spin_lock, but rt_spin_trylock() will > + * mark the task as the owner of another rt_spin_lock which will > + * confuse PI logic, so return immediately if called from hard IRQ or > + * NMI. > + * > + * Note, irqs_disabled() case is ok. spin_trylock() can be called > + * from raw_spin_lock_irqsave region. > + */ > + if (IS_ENABLED(CONFIG_PREEMPT_RT) && (in_nmi() || in_hardirq())) > + return false; > + > + /* On UP, spin_trylock() always succeeds even when it is locked */ > + if (!IS_ENABLED(CONFIG_SMP) && in_nmi()) > + return false; > + > + return true; > +} > + > #endif /* __MM_INTERNAL_H */ > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index c3b246e67ed14..a63733dac659e 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5291,22 +5291,7 @@ static inline bool alloc_order_allowed(gfp_t gfp, unsigned int order, > > static inline bool alloc_nolock_allowed(void) > { > - /* > - * In PREEMPT_RT spin_trylock() will call raw_spin_lock() which is > - * unsafe in NMI. If spin_trylock() is called from hard IRQ the current > - * task may be waiting for one rt_spin_lock, but rt_spin_trylock() will > - * mark the task as the owner of another rt_spin_lock which will > - * confuse PI logic, so return immediately if called from hard IRQ or > - * NMI. > - * > - * Note, irqs_disabled() case is ok. This function can be called > - * from raw_spin_lock_irqsave region. > - */ > - if (IS_ENABLED(CONFIG_PREEMPT_RT) && (in_nmi() || in_hardirq())) > - return false; > - > - /* On UP, spin_trylock() always succeeds even when it is locked */ > - if (!IS_ENABLED(CONFIG_SMP) && in_nmi()) > + if (!can_spin_trylock()) > return false; > > /* Bailout, since _deferred_grow_zone() needs to take a lock */ > diff --git a/mm/slub.c b/mm/slub.c > index 3989b4758ae0a..b19dc46de73c5 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -5408,15 +5408,7 @@ static void *__kmalloc_nolock_noprof(DECL_TOKEN_PARAMS(size, token), gfp_t gfp_f > if (unlikely(!size)) > return ZERO_SIZE_PTR; > > - /* > - * See the comment for the same check in > - * alloc_frozen_pages_nolock_noprof() > - */ > - if (IS_ENABLED(CONFIG_PREEMPT_RT) && (in_nmi() || in_hardirq())) > - return NULL; > - > - /* On UP, spin_trylock() always succeeds even when it is locked */ > - if (!IS_ENABLED(CONFIG_SMP) && in_nmi()) > + if (!can_spin_trylock()) > return NULL; > > retry: >