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 DCAF241760 for ; Tue, 27 Aug 2024 23:57:21 +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=1724803041; cv=none; b=fov+NdqQXe/o9gT5xiEQz/tmeMw0pGRYrWY/v+Qvjsnht9izc+ZOTUDL2w+COC+QLfHTj8RHHqD2eegSbMGId5s4odbfhUWFXlbTOggvcnzv15+Ow9fD3is4OkIaAp/JyqVzBHD894/qYbiCdEoDD3TPbmSBdeEqa4ZfcoW68HM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724803041; c=relaxed/simple; bh=kccdPUYg+HoiZW23Alq5dnCBnPn6xV/ZwJ4GU0c5f8E=; h=Date:To:From:Subject:Message-Id; b=mzs4sQ7MA+qv0JEolIxjX+Ym5oBdNjk6UsHlofcj0utR72N2vi6J04IAVtAW3Yh7nJhx1yBYCEql5PP7u3XwadEmiN2V7I6e+mklb/LHAWwCuPpp4Tz2dV/NqPG7kGFoycEtb5FcwYlCsljK/jDDkLLh1kTX5Pyp2BanbYU4bQA= 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=PkKQV+t6; 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="PkKQV+t6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 60CD2C32782; Tue, 27 Aug 2024 23:57:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1724803041; bh=kccdPUYg+HoiZW23Alq5dnCBnPn6xV/ZwJ4GU0c5f8E=; h=Date:To:From:Subject:From; b=PkKQV+t6IkhnWRs0dje3O2L+O8WePwChSRCAVOkpL7OZsJkSyC5YugwKpGFlEoBo7 uvUqZs5esmd8eTtWtRnhtlxM3IML8IwK2K0gRaobPUHUVR5ZaRNdGgyDSTu2IVLZob mDnEnRK2r9Laj81nvIXX7KhKYysq9H8YXEWcT1WE= Date: Tue, 27 Aug 2024 16:57:20 -0700 To: mm-commits@vger.kernel.org,yosryahmed@google.com,tj@kernel.org,shakeel.butt@linux.dev,roman.gushchin@linux.dev,muchun.song@linux.dev,mkoutny@suse.com,mhocko@kernel.org,lizefan.x@bytedance.com,hannes@cmpxchg.org,kinseyho@google.com,akpm@linux-foundation.org From: Andrew Morton Subject: + cgroup-clarify-css-sibling-linkage-is-protected-by-cgroup_mutex-or-rcu.patch added to mm-unstable branch Message-Id: <20240827235721.60CD2C32782@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: cgroup: clarify css sibling linkage is protected by cgroup_mutex or RCU has been added to the -mm mm-unstable branch. Its filename is cgroup-clarify-css-sibling-linkage-is-protected-by-cgroup_mutex-or-rcu.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/cgroup-clarify-css-sibling-linkage-is-protected-by-cgroup_mutex-or-rcu.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm 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 the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Kinsey Ho Subject: cgroup: clarify css sibling linkage is protected by cgroup_mutex or RCU Date: Tue, 27 Aug 2024 23:07:38 +0000 Pach series "Improve mem_cgroup_iter()", v3. Incremental cgroup iteration is being used again [1]. This patchset improves the reliability of mem_cgroup_iter(). It also improves simplicity and code readability. [1] https://lore.kernel.org/20240514202641.2821494-1-hannes@cmpxchg.org/ This patch (of 5): Explicitly document that css sibling/descendant linkage is protected by cgroup_mutex or RCU. Also, document in css_next_descendant_pre() and similar functions that it isn't necessary to hold a ref on @pos. The following changes in this patchset rely on this clarification for simplification in memcg iteration code. Link: https://lkml.kernel.org/r/20240827230753.2073580-1-kinseyho@google.com Link: https://lkml.kernel.org/r/20240827230753.2073580-2-kinseyho@google.com Suggested-by: Yosry Ahmed Reviewed-by: Michal Koutný Signed-off-by: Kinsey Ho Cc: Johannes Weiner Cc: Michal Hocko Cc: Muchun Song Cc: Roman Gushchin Cc: Shakeel Butt Cc: Tejun Heo Cc: Zefan Li Signed-off-by: Andrew Morton --- include/linux/cgroup-defs.h | 6 +++++- kernel/cgroup/cgroup.c | 16 +++++++++------- 2 files changed, 14 insertions(+), 8 deletions(-) --- a/include/linux/cgroup-defs.h~cgroup-clarify-css-sibling-linkage-is-protected-by-cgroup_mutex-or-rcu +++ a/include/linux/cgroup-defs.h @@ -172,7 +172,11 @@ struct cgroup_subsys_state { /* reference count - access via css_[try]get() and css_put() */ struct percpu_ref refcnt; - /* siblings list anchored at the parent's ->children */ + /* + * siblings list anchored at the parent's ->children + * + * linkage is protected by cgroup_mutex or RCU + */ struct list_head sibling; struct list_head children; --- a/kernel/cgroup/cgroup.c~cgroup-clarify-css-sibling-linkage-is-protected-by-cgroup_mutex-or-rcu +++ a/kernel/cgroup/cgroup.c @@ -4602,8 +4602,9 @@ struct cgroup_subsys_state *css_next_chi * * While this function requires cgroup_mutex or RCU read locking, it * doesn't require the whole traversal to be contained in a single critical - * section. This function will return the correct next descendant as long - * as both @pos and @root are accessible and @pos is a descendant of @root. + * section. Additionally, it isn't necessary to hold onto a reference to @pos. + * This function will return the correct next descendant as long as both @pos + * and @root are accessible and @pos is a descendant of @root. * * If a subsystem synchronizes ->css_online() and the start of iteration, a * css which finished ->css_online() is guaranteed to be visible in the @@ -4651,8 +4652,9 @@ EXPORT_SYMBOL_GPL(css_next_descendant_pr * * While this function requires cgroup_mutex or RCU read locking, it * doesn't require the whole traversal to be contained in a single critical - * section. This function will return the correct rightmost descendant as - * long as @pos is accessible. + * section. Additionally, it isn't necessary to hold onto a reference to @pos. + * This function will return the correct rightmost descendant as long as @pos + * is accessible. */ struct cgroup_subsys_state * css_rightmost_descendant(struct cgroup_subsys_state *pos) @@ -4696,9 +4698,9 @@ css_leftmost_descendant(struct cgroup_su * * While this function requires cgroup_mutex or RCU read locking, it * doesn't require the whole traversal to be contained in a single critical - * section. This function will return the correct next descendant as long - * as both @pos and @cgroup are accessible and @pos is a descendant of - * @cgroup. + * section. Additionally, it isn't necessary to hold onto a reference to @pos. + * This function will return the correct next descendant as long as both @pos + * and @cgroup are accessible and @pos is a descendant of @cgroup. * * If a subsystem synchronizes ->css_online() and the start of iteration, a * css which finished ->css_online() is guaranteed to be visible in the _ Patches currently in -mm which might be from kinseyho@google.com are cgroup-clarify-css-sibling-linkage-is-protected-by-cgroup_mutex-or-rcu.patch mm-dont-hold-css-refcnt-during-traversal.patch mm-increment-gen-before-restarting-traversal.patch mm-restart-if-multiple-traversals-raced.patch mm-clean-up-mem_cgroup_iter.patch