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[209.85.167.49]) by smtp.gmail.com with ESMTPSA id g5sm19845377ljj.69.2019.08.09.15.46.15 for (version=TLS1_3 cipher=AEAD-AES128-GCM-SHA256 bits=128/128); Fri, 09 Aug 2019 15:46:15 -0700 (PDT) Received: by mail-lf1-f49.google.com with SMTP id x3so16830510lfn.6 for ; Fri, 09 Aug 2019 15:46:15 -0700 (PDT) X-Received: by 2002:ac2:5c42:: with SMTP id s2mr14345185lfp.61.1565390774837; Fri, 09 Aug 2019 15:46:14 -0700 (PDT) MIME-Version: 1.0 References: <1565278859475.1962@mentor.com> <1565358624103.3694@mentor.com> <20190809223831.fk4uyrzscr366syr@master> In-Reply-To: <20190809223831.fk4uyrzscr366syr@master> From: Linus Torvalds Date: Fri, 9 Aug 2019 15:45:59 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: Resend [PATCH] kernel/resource.c: invalidate parent when freed resource has childs To: Wei Yang Cc: "Schmid, Carsten" , "bp@suse.de" , "dan.j.williams@intel.com" , "mingo@kernel.org" , "dave.hansen@linux.intel.com" , "linux-kernel@vger.kernel.org" , "bhelgaas@google.com" , "osalvador@suse.de" , "rdunlap@infradead.org" , "richardw.yang@linux.intel.com" , "gregkh@linuxfoundation.org" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 9, 2019 at 3:38 PM Wei Yang wrote: > > In theory, child may have siblings. Would it be possible to have several > devices under xhci-hcd? I'm less interested in the xhci-hcd case - which I certainly *hope* is fixed already? - than in "if this happens somewhere else". So if we do want to remove the parent (which may be a good idea with a warning), and want to make sure that the children are really removed from the resource hierarchy, we should do somethiing like static bool detach_children(struct resource *res) { res = res->child; if (!res) return false; do { res->parent = NULL; res = res->sibling; } while (res); return true; } and then we could write the __release_region() warning as /* You should not release a resource that has children */ WARN_ON_ONCE(detach_children(res)); or something? NOTE! The above is entirely untested, and written purely in my mail reader. It might be seriously buggy, including not compiling, or doing odd things. See it more as a "maybe something like this" code snippet example than any kind of final form. Linus