From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 A00703988F8 for ; Tue, 12 May 2026 22:49:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778626188; cv=none; b=qxzrif8vEwbYIA7u0Pfz1WZ2rgGySC4zYq4KZ/87+I4DAmSlj+W9C+CtOXttvDVAS7OKSA+C8QrlLoPmCeSzG+ISTnJK3K3bDWuuxYO52VAYpGiDc9oHTBRwCp7Y5YB4ab3R/q8SsV7i7h+q4+JvQnmUsC+fpJ6wYOdiS/IX5Hk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778626188; c=relaxed/simple; bh=KmDMWKWkt0P4wRz0g6z2kn2iHIdqjiVa0Y9dzQO+RKw=; h=Date:To:From:Subject:Message-Id; b=Vkf8II/59sypV3w0wIZLnKCxPbj4P/9mF2fmNKCE71i4Ie2VWK+EtPwi1qdPETvSmiq+QgAwNZMBPj/JV4B1uTvEolW0ObOt4bxFzAl/TDsTY41lfVKfTUMoUcdyxl1jrYFf586lVTZ3/x20l3LwpMlEZpJ5PMTvE9xh4R4ld3E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=RghrYIbF; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="RghrYIbF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EE967C2BCB8; Tue, 12 May 2026 22:49:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1778626188; bh=KmDMWKWkt0P4wRz0g6z2kn2iHIdqjiVa0Y9dzQO+RKw=; h=Date:To:From:Subject:From; b=RghrYIbFTPCZT3PEBbjjbZPfMjv9HZOw3Vxkc+Jnqw3b7NDHjmmjceLFnZ+06kAT9 rsF+S8LWl4Z2zwQKlOtQ/o7iDr/20B4O0X5ESGMeRvP2KuyWKw/6vukhh34AwUgaQ6 NVPZykyy/rSd49EQvPKk8Cg/EzegJkrtkIP7LyrE= Date: Tue, 12 May 2026 15:49:36 -0700 To: mm-commits@vger.kernel.org,tj@kernel.org,dodam@google.com,dennis@kernel.org,cl@linux.com,joonwonkang@google.com,akpm@linux-foundation.org From: Andrew Morton Subject: + percpu-do-not-trust-hint-starts-when-they-are-not-set.patch added to mm-new branch Message-Id: <20260512224947.EE967C2BCB8@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: percpu: do not trust hint starts when they are not set has been added to the -mm mm-new branch. Its filename is percpu-do-not-trust-hint-starts-when-they-are-not-set.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/percpu-do-not-trust-hint-starts-when-they-are-not-set.patch This patch will later appear in the mm-new branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Note, mm-new is a provisional staging ground for work-in-progress patches, and acceptance into mm-new is a notification for others take notice and to finish up reviews. Please do not hesitate to respond to review feedback and post updated versions to replace or incrementally fixup patches in mm-new. The mm-new branch of mm.git is not included in linux-next If a few days of testing in mm-new is successful, the patch will me moved into mm.git's mm-unstable branch, which is included in linux-next Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: Joonwon Kang Subject: percpu: do not trust hint starts when they are not set Date: Sun, 10 May 2026 07:21:47 +0000 contig_hint_start can be trusted outside the hint update function since it will be updated everytime contig_hint is broken. On the other hand, scan_hint_start might still be invalid anywhere in the code due to the broken scan_hint not being updated promptly. If those starts are trusted when they are not set, it could lead to false invalidation or update of the hints. Link: https://lore.kernel.org/20260510072149.1279887-2-joonwonkang@google.com Signed-off-by: Joonwon Kang Cc: Christoph Lameter Cc: Dennis Zhou Cc: Tejun Heo Cc: Signed-off-by: Andrew Morton --- mm/percpu.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) --- a/mm/percpu.c~percpu-do-not-trust-hint-starts-when-they-are-not-set +++ a/mm/percpu.c @@ -640,12 +640,13 @@ static void pcpu_block_update(struct pcp if (contig > block->contig_hint) { /* promote the old contig_hint to be the new scan_hint */ - if (start > block->contig_hint_start) { + if (block->contig_hint && start > block->contig_hint_start) { if (block->contig_hint > block->scan_hint) { block->scan_hint_start = block->contig_hint_start; block->scan_hint = block->contig_hint; - } else if (start < block->scan_hint_start) { + } else if (block->scan_hint && + start < block->scan_hint_start) { /* * The old contig_hint == scan_hint. But, the * new contig is larger so hold the invariant @@ -664,10 +665,12 @@ static void pcpu_block_update(struct pcp __ffs(start) > __ffs(block->contig_hint_start))) { /* start has a better alignment so use it */ block->contig_hint_start = start; - if (start < block->scan_hint_start && + if (block->scan_hint && + start < block->scan_hint_start && block->contig_hint > block->scan_hint) block->scan_hint = 0; - } else if (start > block->scan_hint_start || + } else if ((block->scan_hint && + start > block->scan_hint_start) || block->contig_hint > block->scan_hint) { /* * Knowing contig == contig_hint, update the scan_hint @@ -845,7 +848,8 @@ static void pcpu_block_update_hint_alloc PCPU_BITMAP_BLOCK_BITS, s_off + bits); - if (pcpu_region_overlap(s_block->scan_hint_start, + if (s_block->scan_hint && + pcpu_region_overlap(s_block->scan_hint_start, s_block->scan_hint_start + s_block->scan_hint, s_off, s_off + bits)) @@ -889,7 +893,8 @@ static void pcpu_block_update_hint_alloc /* reset the block */ e_block++; } else { - if (e_off > e_block->scan_hint_start) + if (e_block->scan_hint && + e_off > e_block->scan_hint_start) e_block->scan_hint = 0; e_block->left_free = 0; @@ -922,7 +927,8 @@ static void pcpu_block_update_hint_alloc if (nr_empty_pages) pcpu_update_empty_pages(chunk, -nr_empty_pages); - if (pcpu_region_overlap(chunk_md->scan_hint_start, + if (chunk_md->scan_hint && + pcpu_region_overlap(chunk_md->scan_hint_start, chunk_md->scan_hint_start + chunk_md->scan_hint, bit_off, _ Patches currently in -mm which might be from joonwonkang@google.com are percpu-fix-wrong-chunk-hints-update.patch percpu-do-not-trust-hint-starts-when-they-are-not-set.patch percpu-introduce-struct-pcpu_region.patch percpu-fix-hint-invariant-breakage.patch