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 7F2FE1E511; Mon, 6 Oct 2025 17:01:48 +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=1759770110; cv=none; b=SB1M9pubQ3hsMM7LApXrnEDbdIMlz5ebs1lXC7WdmbkwjAragc/HmBmg2o2mUH0I5seIv427u0ncrobgYV16p3JVOl7U05Pk8IGe7WgGfocYh+J8NJhsGRzRp+TP66n0IpPZo85uRT/VkleyfbsTHROWlpkAvf7GJNnWryEL3hU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759770110; c=relaxed/simple; bh=MG1dcQMphQ748JndS811tTZbOvZl5viKUiBdA36kux8=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=iJOQyagk1PvCjlFhH6MMCWYochbzXFCk/Nu/p/YW47Bi3n2IoOVb/LFDEDlG8MwqBB8WTZSMnxu03Kej0mjNWcgQC5ge4xyx71EpYsa1dpIj+fHiUVvGaRF+Uy+4Tyz2mfRsIfZBjxAvUR115++M4pNZXNoLFfU+b8gC0zouGaE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NgLfsYlT; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="NgLfsYlT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A2E62C4CEF5; Mon, 6 Oct 2025 17:01:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1759770108; bh=MG1dcQMphQ748JndS811tTZbOvZl5viKUiBdA36kux8=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=NgLfsYlTgtpvDbSOm2NiGUojPOjwRGe/OH3C0JNNWeU0NeJOo51dJ2Ci9kDtEdQQe 3k5DscndvUU0phiQ/ZHNvwhZrgX6lqwI5J/xlNMT8aZdV5u3WDO3VM8ATPykvRSGGT r5b1d+SHy8/FqS7MKcd7EdWJCNFHUCHjE9sfR1Z8e+WnV6oVs1zsX8KGWKj3S8B7Ik dfqxPViKr/BDk3+rzxCGaCa3H0MaJSLU2n1ptlHIv/2Y1ql7EfqnzAbEI1HB2hxOHp 1IF9IgN+pr/DVwtODnsjwyUKJ4s19AHLk26ebEq26WDj2aZOB2f8yyO+hVGm27x+7w a51lxbN5OsjFQ== From: Pratyush Yadav To: Pasha Tatashin Cc: pratyush@kernel.org, jasonmiu@google.com, graf@amazon.com, changyuanl@google.com, rppt@kernel.org, dmatlack@google.com, rientjes@google.com, corbet@lwn.net, rdunlap@infradead.org, ilpo.jarvinen@linux.intel.com, kanie@linux.alibaba.com, ojeda@kernel.org, aliceryhl@google.com, masahiroy@kernel.org, akpm@linux-foundation.org, tj@kernel.org, yoann.congal@smile.fr, mmaurer@google.com, roman.gushchin@linux.dev, chenridong@huawei.com, axboe@kernel.dk, mark.rutland@arm.com, jannh@google.com, vincent.guittot@linaro.org, hannes@cmpxchg.org, dan.j.williams@intel.com, david@redhat.com, joel.granados@kernel.org, rostedt@goodmis.org, anna.schumaker@oracle.com, song@kernel.org, zhangguopeng@kylinos.cn, linux@weissschuh.net, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, gregkh@linuxfoundation.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, rafael@kernel.org, dakr@kernel.org, bartosz.golaszewski@linaro.org, cw00.choi@samsung.com, myungjoo.ham@samsung.com, yesanishhere@gmail.com, Jonathan.Cameron@huawei.com, quic_zijuhu@quicinc.com, aleksander.lobakin@intel.com, ira.weiny@intel.com, andriy.shevchenko@linux.intel.com, leon@kernel.org, lukas@wunner.de, bhelgaas@google.com, wagi@kernel.org, djeffery@redhat.com, stuart.w.hayes@gmail.com, lennart@poettering.net, brauner@kernel.org, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, saeedm@nvidia.com, ajayachandra@nvidia.com, jgg@nvidia.com, parav@nvidia.com, leonro@nvidia.com, witu@nvidia.com, hughd@google.com, skhawaja@google.com, chrisl@kernel.org, steven.sistare@oracle.com Subject: Re: [PATCH v4 03/30] kho: drop notifiers In-Reply-To: <20250929010321.3462457-4-pasha.tatashin@soleen.com> (Pasha Tatashin's message of "Mon, 29 Sep 2025 01:02:54 +0000") References: <20250929010321.3462457-1-pasha.tatashin@soleen.com> <20250929010321.3462457-4-pasha.tatashin@soleen.com> Date: Mon, 06 Oct 2025 19:01:37 +0200 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Mon, Sep 29 2025, Pasha Tatashin wrote: > From: "Mike Rapoport (Microsoft)" > > The KHO framework uses a notifier chain as the mechanism for clients to > participate in the finalization process. While this works for a single, > central state machine, it is too restrictive for kernel-internal > components like pstore/reserve_mem or IMA. These components need a > simpler, direct way to register their state for preservation (e.g., > during their initcall) without being part of a complex, > shutdown-time notifier sequence. The notifier model forces all > participants into a single finalization flow and makes direct > preservation from an arbitrary context difficult. > This patch refactors the client participation model by removing the > notifier chain and introducing a direct API for managing FDT subtrees. > > The core kho_finalize() and kho_abort() state machine remains, but > clients now register their data with KHO beforehand. > > Signed-off-by: Mike Rapoport (Microsoft) > Signed-off-by: Pasha Tatashin [...] > diff --git a/mm/memblock.c b/mm/memblock.c > index e23e16618e9b..c4b2d4e4c715 100644 > --- a/mm/memblock.c > +++ b/mm/memblock.c > @@ -2444,53 +2444,18 @@ int reserve_mem_release_by_name(const char *name) > #define MEMBLOCK_KHO_FDT "memblock" > #define MEMBLOCK_KHO_NODE_COMPATIBLE "memblock-v1" > #define RESERVE_MEM_KHO_NODE_COMPATIBLE "reserve-mem-v1" > -static struct page *kho_fdt; > - > -static int reserve_mem_kho_finalize(struct kho_serialization *ser) > -{ > - int err = 0, i; > - > - for (i = 0; i < reserved_mem_count; i++) { > - struct reserve_mem_table *map = &reserved_mem_table[i]; > - struct page *page = phys_to_page(map->start); > - unsigned int nr_pages = map->size >> PAGE_SHIFT; > - > - err |= kho_preserve_pages(page, nr_pages); > - } > - > - err |= kho_preserve_folio(page_folio(kho_fdt)); > - err |= kho_add_subtree(ser, MEMBLOCK_KHO_FDT, page_to_virt(kho_fdt)); > - > - return notifier_from_errno(err); > -} > - > -static int reserve_mem_kho_notifier(struct notifier_block *self, > - unsigned long cmd, void *v) > -{ > - switch (cmd) { > - case KEXEC_KHO_FINALIZE: > - return reserve_mem_kho_finalize((struct kho_serialization *)v); > - case KEXEC_KHO_ABORT: > - return NOTIFY_DONE; > - default: > - return NOTIFY_BAD; > - } > -} > - > -static struct notifier_block reserve_mem_kho_nb = { > - .notifier_call = reserve_mem_kho_notifier, > -}; > > static int __init prepare_kho_fdt(void) > { > int err = 0, i; > + struct page *fdt_page; > void *fdt; > > - kho_fdt = alloc_page(GFP_KERNEL); > - if (!kho_fdt) > + fdt_page = alloc_page(GFP_KERNEL); > + if (!fdt_page) > return -ENOMEM; > > - fdt = page_to_virt(kho_fdt); > + fdt = page_to_virt(fdt_page); > > err |= fdt_create(fdt, PAGE_SIZE); > err |= fdt_finish_reservemap(fdt); > @@ -2499,7 +2464,10 @@ static int __init prepare_kho_fdt(void) > err |= fdt_property_string(fdt, "compatible", MEMBLOCK_KHO_NODE_COMPATIBLE); > for (i = 0; i < reserved_mem_count; i++) { > struct reserve_mem_table *map = &reserved_mem_table[i]; > + struct page *page = phys_to_page(map->start); > + unsigned int nr_pages = map->size >> PAGE_SHIFT; > > + err |= kho_preserve_pages(page, nr_pages); > err |= fdt_begin_node(fdt, map->name); > err |= fdt_property_string(fdt, "compatible", RESERVE_MEM_KHO_NODE_COMPATIBLE); > err |= fdt_property(fdt, "start", &map->start, sizeof(map->start)); > @@ -2507,13 +2475,14 @@ static int __init prepare_kho_fdt(void) > err |= fdt_end_node(fdt); > } > err |= fdt_end_node(fdt); > - > err |= fdt_finish(fdt); > > + err |= kho_preserve_folio(page_folio(fdt_page)); > + err |= kho_add_subtree(MEMBLOCK_KHO_FDT, fdt); > + > if (err) { > pr_err("failed to prepare memblock FDT for KHO: %d\n", err); > - put_page(kho_fdt); > - kho_fdt = NULL; > + put_page(fdt_page); This adds subtree to KHO even if the FDT might be invalid. And then leaves a dangling reference in KHO to the FDT in case of an error. I think you should either do this check after kho_preserve_folio(page_folio(fdt_page)) and do a clean error check for kho_add_subtree(), or call kho_remove_subtree() in the error block. I prefer the former since if kho_add_subtree() is the one that fails, there is little sense in removing a subtree that was never added. > } > > return err; > @@ -2529,13 +2498,6 @@ static int __init reserve_mem_init(void) > err = prepare_kho_fdt(); > if (err) > return err; > - > - err = register_kho_notifier(&reserve_mem_kho_nb); > - if (err) { > - put_page(kho_fdt); > - kho_fdt = NULL; > - } > - > return err; > } > late_initcall(reserve_mem_init); -- Regards, Pratyush Yadav