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 D744F17BEBF for ; Tue, 10 Feb 2026 13:30:48 +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=1770730248; cv=none; b=LuPzkMbZXJMQ5fG92LMkqjLQThXgJZUY47etERTZYoU+T5Vtd6NgPW1Un+3arNedsIuvExshd4/zesTEbIhKujdZx6ENHFDrjtDEocKVTm69hXFcJr3SabGHI8N8wHXYD+e7tf4YSISWMUnu4tb30u91Tg+RkEAd/E1Sm8m2wpI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770730248; c=relaxed/simple; bh=tFOyTVhR+WU/OkMF4qkv7WslBiNhFBOO/Y7SpuCXXwk=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=fnj2BhTY9HIAGsVX+TBDFmPb01PgDa8lqYjnzwa2mN5Pb5fhISMqea1EV1R5pszSzv2+Q39wffHNe1VQ2R+bpqHz3eOr9j1e+/kGyW+b+EUIGVfk7R+eSy8zmTERiI3yvBDywqk9Uegr4iYht2OB1uIgBKqpojgB7zMd3NURr9s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=q+KMZT6u; 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="q+KMZT6u" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5AE95C116C6; Tue, 10 Feb 2026 13:30:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770730248; bh=tFOyTVhR+WU/OkMF4qkv7WslBiNhFBOO/Y7SpuCXXwk=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=q+KMZT6uGMPekyGMrCG4ahzu+wWRYsoPqQ7zO4ONkJ78fzq87BqZDvFgxphBGDdVJ ZK1o3eUvKE8YHbFFeY90FmOVnGh2VZLImCjghnJ//SkZMvdvLgCXY8wH8OAruoEYYm 1Wdh22uw6fmf3GZubBv/kS5gXg7qT4SfC+uQqo2Pl8YJUoC4t9J6IObqi16XJbI98U 0/n4eSKrQoKjuWP5AjAKI2T8dn2MJ+/Z/3DfAuydeUIJOg1B9mazxPtzGDolDAEIq6 IlkQaWO20DvSOWdIUgqprUQeSrS1/433CMo2J5/EBkNjiCArWr4wjA0oMaYlAjVfJO owSOBNTwlgCfw== From: Pratyush Yadav To: Mike Rapoport Cc: Pratyush Yadav , Pasha Tatashin , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 2/2] liveupdate: luo_file: remember retrieve() status In-Reply-To: (Mike Rapoport's message of "Wed, 28 Jan 2026 13:37:08 +0200") References: <20260126230302.2936817-1-pratyush@kernel.org> <20260126230302.2936817-3-pratyush@kernel.org> Date: Tue, 10 Feb 2026 14:30:45 +0100 Message-ID: <2vxzfr78u3ne.fsf@kernel.org> User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Hi Mike, Thanks for the review. On Wed, Jan 28 2026, Mike Rapoport wrote: > Hi Pratyush, > > On Tue, Jan 27, 2026 at 12:02:53AM +0100, Pratyush Yadav wrote: >> From: "Pratyush Yadav (Google)" >> >> LUO keeps track of successful retrieve attempts on a LUO file. It does >> so to avoid multiple retrievals of the same file. Doing so will cause > > ^ Multiple retrievals Will fix. > >> problems because once the file is retrieved, the serialized data >> structures are likely freed and the file is likely in a very different >> state from what the code expects. >> >> This is kept track of by the retrieved boolean in struct luo_file, and > > The 'retrieve' boolean in struct luo_file keeps track of this, ACK. > >> is passed to the finish callback so it knows what work was already done >> and what it has left to do. >> >> All this works well when retrieve succeeds. When it fails, >> luo_retrieve_file() returns the error immediately, without ever storing >> anywhere that a retrieve was attempted or what its error code was. This >> results in an errored LIVEUPDATE_SESSION_RETRIEVE_FD ioctl to userspace, >> but nothing prevents it from trying this again. >> >> The retry is problematic for much of the same reasons listed above. The >> file is likely in a very different state than what the retrieve logic >> normally expects, and it might even have freed some serialization data >> structures. Attempting to access them or free them again is going to >> break things. >> >> For example, if memfd managed to restore 8 of its 10 folios, but fails >> on the 9th, a subsequent retrieve attempt will try to call >> kho_restore_folio() on the first folio again, and that will fail with a >> warning since it is an invalid operation. >> >> Apart from the retry, finish() also breaks. Since on failure the >> retrieved bool in luo_file is never touched, the finish() call on >> session close will tell the file handler that retrieve was never >> attempted, and it will try to access or free the data structures that >> might not exist, much in the same way as the retry attempt. >> >> There is no sane way of attempting the retrieve again. Remember the >> error retrieve returned and directly return it on a retry. Also pass >> this status code to finish() so it can make the right decision on the >> work it needs to do. >> >> This is done by changing the bool to an integer. A value of 0 means >> retrieve was never attempted, a positive value means it succeeded, and a >> negative value means it failed and the error code is the value. >> >> Fixes: 7c722a7f44e0 ("liveupdate: luo_file: implement file systems callbacks") >> Signed-off-by: Pratyush Yadav (Google) >> --- >> include/linux/liveupdate.h | 7 ++++-- >> kernel/liveupdate/luo_file.c | 41 ++++++++++++++++++++++-------------- >> mm/memfd_luo.c | 7 +++++- >> 3 files changed, 36 insertions(+), 19 deletions(-) >> >> diff --git a/include/linux/liveupdate.h b/include/linux/liveupdate.h >> index a7f6ee5b6771..a543a3a8e837 100644 >> --- a/include/linux/liveupdate.h >> +++ b/include/linux/liveupdate.h >> @@ -21,7 +21,10 @@ struct file; >> * struct liveupdate_file_op_args - Arguments for file operation callbacks. >> * @handler: The file handler being called. >> * @retrieved: The retrieve status for the 'can_finish / finish' >> - * operation. >> + * operation. A value of 0 means the retrieve has not been >> + * attempted, a positive value means the retrieve was >> + * successful, and a negative value means the retrieve failed, >> + * and the value is the error code of the call. >> * @file: The file object. For retrieve: [OUT] The callback sets >> * this to the new file. For other ops: [IN] The caller sets >> * this to the file being operated on. >> @@ -37,7 +40,7 @@ struct file; >> */ >> struct liveupdate_file_op_args { >> struct liveupdate_file_handler *handler; >> - bool retrieved; >> + bool retrieve_sts; > > int retrieve_sts? Ugh, stupid mistake... Thanks for catching. > > and maybe spell out _status rather than _sts? Will do. > >> struct file *file; >> u64 serialized_data; >> void *private_data; >> diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c >> index 9f7283379ebc..82577b4cca2b 100644 >> --- a/kernel/liveupdate/luo_file.c >> +++ b/kernel/liveupdate/luo_file.c >> @@ -133,9 +133,12 @@ static LIST_HEAD(luo_file_handler_list); >> * state that is not preserved. Set by the handler's .preserve() >> * callback, and must be freed in the handler's .unpreserve() >> * callback. >> - * @retrieved: A flag indicating whether a user/kernel in the new kernel has >> + * @retrieve_sts: Status code indicating whether a user/kernel in the new kernel has >> * successfully called retrieve() on this file. This prevents >> - * multiple retrieval attempts. >> + * multiple retrieval attempts. A value of 0 means a retrieve() >> + * has not been attempted, a positive value means the retrieve() >> + * was successful, and a negative value means the retrieve() >> + * failed, and the value is the error code of the call. >> * @mutex: A mutex that protects the fields of this specific instance >> * (e.g., @retrieved, @file), ensuring that operations like >> * retrieving or finishing a file are atomic. >> @@ -160,7 +163,7 @@ struct luo_file { >> struct file *file; >> u64 serialized_data; >> void *private_data; >> - bool retrieved; >> + int retrieve_sts; >> struct mutex mutex; >> struct list_head list; >> u64 token; >> @@ -293,7 +296,7 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd) >> luo_file->file = file; >> luo_file->fh = fh; >> luo_file->token = token; >> - luo_file->retrieved = false; >> + luo_file->retrieve_sts = 0; > > We kzalloc() luo_file, so this is not strictly required. Okay, will drop. > >> mutex_init(&luo_file->mutex); >> >> args.handler = fh; >> @@ -569,7 +572,7 @@ int luo_retrieve_file(struct luo_file_set *file_set, u64 token, >> return -ENOENT; >> >> guard(mutex)(&luo_file->mutex); >> - if (luo_file->retrieved) { >> + if (luo_file->retrieve_sts > 0) { >> /* >> * Someone is asking for this file again, so get a reference >> * for them. >> @@ -577,21 +580,27 @@ int luo_retrieve_file(struct luo_file_set *file_set, u64 token, >> get_file(luo_file->file); >> *filep = luo_file->file; >> return 0; >> + } else if (luo_file->retrieve_sts < 0) { >> + /* Retrieve was attempted and it failed. Return the error code. */ >> + return luo_file->retrieve_sts; >> } > > I'd put it before the check for > 0, i.e > > if (luo_file->retrieve_sts < 0) > return luo_file->retrieve_sts; > > if (luo_file->retrieve_sts > 0) > ... ACK. Will do. > > >> args.handler = luo_file->fh; >> args.serialized_data = luo_file->serialized_data; >> err = luo_file->fh->ops->retrieve(&args); >> - if (!err) { >> - luo_file->file = args.file; >> - >> - /* Get reference so we can keep this file in LUO until finish */ >> - get_file(luo_file->file); >> - *filep = luo_file->file; >> - luo_file->retrieved = true; >> + if (err) { >> + /* Keep the error code for later use. */ >> + luo_file->retrieve_sts = err; >> + return err; >> } >> >> - return err; >> + luo_file->file = args.file; >> + /* Get reference so we can keep this file in LUO until finish */ >> + get_file(luo_file->file); >> + *filep = luo_file->file; >> + luo_file->retrieve_sts = 1; >> + >> + return 0; >> } >> >> static int luo_file_can_finish_one(struct luo_file_set *file_set, >> @@ -607,7 +616,7 @@ static int luo_file_can_finish_one(struct luo_file_set *file_set, >> args.handler = luo_file->fh; >> args.file = luo_file->file; >> args.serialized_data = luo_file->serialized_data; >> - args.retrieved = luo_file->retrieved; >> + args.retrieve_sts = luo_file->retrieve_sts; >> can_finish = luo_file->fh->ops->can_finish(&args); >> } >> >> @@ -624,7 +633,7 @@ static void luo_file_finish_one(struct luo_file_set *file_set, >> args.handler = luo_file->fh; >> args.file = luo_file->file; >> args.serialized_data = luo_file->serialized_data; >> - args.retrieved = luo_file->retrieved; >> + args.retrieve_sts = luo_file->retrieve_sts; >> >> luo_file->fh->ops->finish(&args); >> } >> @@ -779,7 +788,7 @@ int luo_file_deserialize(struct luo_file_set *file_set, >> luo_file->file = NULL; >> luo_file->serialized_data = file_ser[i].data; >> luo_file->token = file_ser[i].token; >> - luo_file->retrieved = false; >> + luo_file->retrieve_sts = 0; > > Here as well, we kzalloc() luo_file, so zeroing out of the fields is not > strictly required. ACK. > >> mutex_init(&luo_file->mutex); >> list_add_tail(&luo_file->list, &file_set->files_list); >> } >> diff --git a/mm/memfd_luo.c b/mm/memfd_luo.c >> index a34fccc23b6a..ffc9f879833b 100644 >> --- a/mm/memfd_luo.c >> +++ b/mm/memfd_luo.c >> @@ -326,7 +326,12 @@ static void memfd_luo_finish(struct liveupdate_file_op_args *args) >> struct memfd_luo_folio_ser *folios_ser; >> struct memfd_luo_ser *ser; >> >> - if (args->retrieved) >> + /* >> + * If retrieve was successful, nothing to do. If it failed, retrieve() >> + * already cleaned up everything it could. So nothing to do there >> + * either. Only need to clean up when retrieve was not called. >> + */ >> + if (args->retrieve_sts) >> return; >> >> ser = phys_to_virt(args->serialized_data); >> -- >> 2.52.0.457.g6b5491de43-goog >> -- Regards, Pratyush Yadav