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 888703D349C for ; Tue, 16 Jun 2026 05:53:17 +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=1781589198; cv=none; b=EEbVyeFm7Rvp+4YpTD77w3EqTtOqWWi8MkpLNPGwAGzhpkT87b6gW6+wZNFFonTJDyLWWgEvi8t92mYycu6JCK/a5YOFXzDbZWL36Dr5AEvkqYt9h424bkbpCdUKMbokGcG/gCkOUMBZgz4hUxC3f+ooPJ09OGf16IS2bLkFR44= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781589198; c=relaxed/simple; bh=iV0KB09rbA+miQouw4pfFUUV9jkRX9iaS7d6UwlRQp4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=RbDvhKuC5kyy8veZs1Uch9puCC4z+ndXD22e+MiJ0iWnP5JgqEy1AuG7G51I9P/UKB9wpyWcWstNAgcHgCg98vs3Vb92HLqSsqEbbi47zH2yjh0Ck77WWjCHfXonRAJRJGs2e6CFBdd746fVxWX3u6b/GLuJohGSp73UHohT4z8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Etpea4I+; 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="Etpea4I+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 94AA61F000E9; Tue, 16 Jun 2026 05:53:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781589197; bh=tAmd5f6Fvl//1hLp2J0FrU4v/ahKgLOpwamh6GzeHs8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Etpea4I+yovK0CPFS2QxaGqDini2Pb42S04Nv/H9HE24lZIjCE3/TPuQtnCeznNXC FE11Rze+vL2gzr3pH6gBE1G/090KBulPIsTj7B1JLK1SG2QrnH2a31q89fpWytH8Hd qt9C3mbZIAp8nXLdQAP26YI2zxpyYmHarXkB5l2PIq4kinI69m6Lepp3xR0Rwt2a08 1p0hoGFpbQDBzI5ZvrhB22BPzVNOQYPPj/lb0o5Cq2FRo3YFRXxeLIoP5ohoAVz0tM 9tmi4SFKGiLw31aYrHungsnji9M4Mh6riYRl2MyMy77eTLi8tXp5BrPdcyaH3i2CRL ZBz0jq755zqtg== Message-ID: <4983aced-49ae-4440-828c-09231b344be8@kernel.org> Date: Tue, 16 Jun 2026 07:53:13 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/percpu: avoid IO dependency in alloc_percpu To: Khazhy Kumykov , Andrew Morton , Michal Hocko , Christoph Lameter , Tejun Heo , Dennis Zhou , Kaitao Cheng Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260616012236.3799518-1-khazhy@google.com> From: "Vlastimil Babka (SUSE)" Content-Language: en-US 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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 6/16/26 04:08, Khazhy Kumykov wrote: > On Mon, Jun 15, 2026 at 6:23 PM Khazhismel Kumykov wrote: >> >> percpu_alloc users within noio context may block on other percpu_alloc >> users doing IO due to the shared pcpu_alloc_mutex. pcpu_balance_workfn >> already grabs under noio context - update remaining holders to also run >> under noio. >> >> Lockdep reported this as a circular locking dependency, with one caller >> having entered fs_reclaim holding pcpu_alloc_mutex, and the second >> caller (elevator init) grabbing pcpu_alloc_mutex in noio context. >> >> Fixes: 9a5b183941b5 ("mm, percpu: do not consider sleepable allocations atomic") >> >> Signed-off-by: Khazhismel Kumykov >> --- >> mm/percpu.c | 9 +++++++-- >> 1 file changed, 7 insertions(+), 2 deletions(-) >> >> diff --git a/mm/percpu.c b/mm/percpu.c >> index b0676b8054ed..50057403ae79 100644 >> --- a/mm/percpu.c >> +++ b/mm/percpu.c >> @@ -1749,8 +1749,13 @@ void __percpu *pcpu_alloc_noprof(size_t size, size_t align, bool reserved, >> size_t bits, bit_align; >> >> gfp = current_gfp_context(gfp); >> - /* whitelisted flags that can be passed to the backing allocators */ >> - pcpu_gfp = gfp & (GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN); >> + /* >> + * whitelisted flags that can be passed to the backing allocators. >> + * >> + * Allocations must be GFP_NOIO, else users in noio/nofs contexts may >> + * form dependency through pcpu_alloc_mutex >> + */ >> + pcpu_gfp = gfp & (GFP_NOIO | __GFP_NORETRY | __GFP_NOWARN); > ah, this is incomplete since we have subsequent allocations that use > "GFP_KERNEL", I'll send a version with memalloc_noio instead. > Apologies... Please see https://lore.kernel.org/all/20260612022648.13008-1-kaitao.cheng@linux.dev/ >> is_atomic = !gfpflags_allow_blocking(gfp); >> do_warn = !(gfp & __GFP_NOWARN); >> >> -- >> 2.54.0.1189.g8c84645362-goog >>