From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 867C6CD4F3C for ; Wed, 4 Sep 2024 22:22:01 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DFC276B00A0; Wed, 4 Sep 2024 18:22:00 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DAA486B00AE; Wed, 4 Sep 2024 18:22:00 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C4B0F6B00B2; Wed, 4 Sep 2024 18:22:00 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id A20B76B00A0 for ; Wed, 4 Sep 2024 18:22:00 -0400 (EDT) Received: from smtpin28.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 466D31A1607 for ; Wed, 4 Sep 2024 22:22:00 +0000 (UTC) X-FDA: 82528479600.28.6080375 Received: from out-173.mta0.migadu.com (out-173.mta0.migadu.com [91.218.175.173]) by imf24.hostedemail.com (Postfix) with ESMTP id 559E8180016 for ; Wed, 4 Sep 2024 22:21:58 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=r7tUoSfo; spf=pass (imf24.hostedemail.com: domain of martin.lau@linux.dev designates 91.218.175.173 as permitted sender) smtp.mailfrom=martin.lau@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1725488442; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=I878VpUdVTEx9+klbDYSkj67bfJZkb3Se/53OB4PWH4=; b=aqOttK4RW3w2dnuHyKT6XZrZFbjj0eGLHqvS8DrVJXhKbUtJUQpawwxc/09uOAirH54pNI TVV6IVJX6YahYT5qN8yYH6qN4JzD+LPV5GAENenP/NdY8kJGHjc5AzGBbH4x4K979e0rox 9lX5kzJBE+OBL7WvcYxJgotgeDSsLGU= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=r7tUoSfo; spf=pass (imf24.hostedemail.com: domain of martin.lau@linux.dev designates 91.218.175.173 as permitted sender) smtp.mailfrom=martin.lau@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1725488442; a=rsa-sha256; cv=none; b=i8ZmSNKBX2ocRagusdAzPkHvARG1NVHH0Hwmpy+dzldxM2wLcYNd9PD5zorxEGrxu387CQ 8QWdOpZSQf1/tloKV16yd8FCOZLNwrkd8gVGHrO1zbqFL99X6c7V2ZoGyf+nD/0BR65IAP eaVTNXxzOvwxxLiN10O8hWm/+PO6iOA= Message-ID: <70a1b24f-84cd-464c-8fb6-a2c52fd3d703@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1725488516; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=I878VpUdVTEx9+klbDYSkj67bfJZkb3Se/53OB4PWH4=; b=r7tUoSfoO7hLnMU1AaKbR7QUDnc4c4US7CLqE4h10TocClvJjdyg/bt8tihKfCAOoJuJBI OUTXmzfNuN0SYrDHx4BHIcAB8uoQSfqIxX+97lm8M4+Xf1G1BFRZZAgIkVa1eM+uVzCr7z qJOVWhW/rTixtZfoQ5YnKYaPG9nQ//o= Date: Wed, 4 Sep 2024 15:21:49 -0700 MIME-Version: 1.0 Subject: Re: [RFC bpf-next v4 4/6] bpf: pin, translate, and unpin __uptr from syscalls. To: Alexei Starovoitov , Kui-Feng Lee Cc: bpf , Alexei Starovoitov , Andrii Nakryiko , Kui-Feng Lee , linux-mm References: <20240816191213.35573-1-thinker.li@gmail.com> <20240816191213.35573-5-thinker.li@gmail.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Martin KaFai Lau Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: 8sbwn9ifd8ciqf7469s87uwuwe1wys8q X-Rspam-User: X-Rspamd-Queue-Id: 559E8180016 X-Rspamd-Server: rspam02 X-HE-Tag: 1725488518-216990 X-HE-Meta: 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 oSrZEN3y GDHpewINuX4hELo5cA7lVzphXzzzDGekVP0QsDuqm52piS+v40vRlXDnyAajVbb062hMj2mwkw1LCleWEFcgEKNJP4ZYJQjSCX3TMBE0m9K3/VMhT/9qaZp6eRgN7LD2M+tm7JnyClYW8Mnz091v6fdvEsHMAjHgNr1mnsZxch3ChJSHqh26/oiI+Efro0JhT2/xOCymt3wHEP4RSaL40C75F8cY8s1JV9Yes X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/28/24 4:24 PM, Alexei Starovoitov wrote: >> @@ -714,6 +869,11 @@ void bpf_obj_free_fields(const struct btf_record *rec, void *obj) >> field->kptr.dtor(xchgd_field); >> } >> break; >> + case BPF_UPTR: >> + if (*(void **)field_ptr) >> + bpf_obj_unpin_uptr(field, *(void **)field_ptr); >> + *(void **)field_ptr = NULL; > This one will be called from > task_storage_delete->bpf_selem_free->bpf_obj_free_fields > > and even if upin was safe to do from that context > we cannot just do: > *(void **)field_ptr = NULL; > > since bpf prog might be running in parallel, > it could have just read that addr and now is using it. > > The first thought of a way to fix this was to split > bpf_obj_free_fields() into the current one plus > bpf_obj_free_fields_after_gp() > that will do the above unpin bit. > and call the later one from bpf_selem_free_rcu() > while bpf_obj_free_fields() from bpf_selem_free() > will not touch uptr. > > But after digging further I realized that task_storage > already switched to use bpf_ma, so the above won't work. > > So we need something similar to BPF_KPTR_REF logic: > xchgd_field = (void *)xchg((unsigned long *)field_ptr, 0); > and then delay of uptr unpin for that address into call_rcu. > > Any better ideas? Many thanks to Kui-Feng starting this useful work on task storage. I will think about it and respin the set.