From mboxrd@z Thu Jan 1 00:00:00 1970 From: Frank Rowand Subject: Re: [PATCH 2/2] of: __of_detach_node() - remove node from phandle cache Date: Fri, 14 Dec 2018 14:38:20 -0800 Message-ID: <878c5024-c184-12f3-2868-df6c79d568ce@gmail.com> References: <1544769771-5468-1-git-send-email-frowand.list@gmail.com> <1544769771-5468-3-git-send-email-frowand.list@gmail.com> <68a9e834-b11d-8b9f-1669-466709257f37@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <68a9e834-b11d-8b9f-1669-466709257f37@linux.vnet.ibm.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Michael Bringmann , Rob Herring Cc: linuxppc-dev , Michael Ellerman , Tyrel Datwyler , tlfalcon@linux.vnet.ibm.com, minkim@us.ibm.com, devicetree@vger.kernel.org, "linux-kernel@vger.kernel.org" , Frank Rowand List-Id: devicetree@vger.kernel.org On 12/14/18 1:56 PM, Michael Bringmann wrote: > On 12/14/2018 11:20 AM, Rob Herring wrote: >> On Fri, Dec 14, 2018 at 12:43 AM wrote: >>> >>> From: Frank Rowand >>> >>> Non-overlay dynamic devicetree node removal may leave the node in >>> the phandle cache. Subsequent calls to of_find_node_by_phandle() >>> will incorrectly find the stale entry. Remove the node from the >>> cache. >>> >>> Add paranoia checks in of_find_node_by_phandle() as a second level >>> of defense (do not return cached node if detached, do not add node >>> to cache if detached). >>> >>> Reported-by: Michael Bringmann >>> Signed-off-by: Frank Rowand >>> --- >>> drivers/of/base.c | 29 ++++++++++++++++++++++++++++- >>> drivers/of/dynamic.c | 3 +++ >>> drivers/of/of_private.h | 4 ++++ >>> 3 files changed, 35 insertions(+), 1 deletion(-) >>> >>> diff --git a/drivers/of/base.c b/drivers/of/base.c >>> index d599367cb92a..34a5125713c8 100644 >>> --- a/drivers/of/base.c >>> +++ b/drivers/of/base.c >>> @@ -162,6 +162,27 @@ int of_free_phandle_cache(void) >>> late_initcall_sync(of_free_phandle_cache); >>> #endif >>> >>> +/* >>> + * Caller must hold devtree_lock. >>> + */ >>> +void __of_free_phandle_cache_entry(phandle handle) >>> +{ >>> + phandle masked_handle; >>> + >>> + if (!handle) >>> + return; >>> + >>> + masked_handle = handle & phandle_cache_mask; >>> + >>> + if (phandle_cache) { >>> + if (phandle_cache[masked_handle] && >>> + handle == phandle_cache[masked_handle]->phandle) { >>> + of_node_put(phandle_cache[masked_handle]); >>> + phandle_cache[masked_handle] = NULL; >>> + } >>> + } >>> +} >>> + >>> void of_populate_phandle_cache(void) >>> { >>> unsigned long flags; >>> @@ -1209,11 +1230,17 @@ struct device_node *of_find_node_by_phandle(phandle handle) >>> if (phandle_cache[masked_handle] && >>> handle == phandle_cache[masked_handle]->phandle) >>> np = phandle_cache[masked_handle]; >>> + if (np && of_node_check_flag(np, OF_DETACHED)) { >>> + of_node_put(np); >>> + phandle_cache[masked_handle] = NULL; >> >> This should never happen, right? Any time we set OF_DETACHED, the >> entry should get removed from the cache. I think we want a WARN here >> in case we're in an unexpected state. Correct, this should never happen. I will add the WARN. > We don't actually remove the pointer from the phandle cache when we set > OF_DETACHED in drivers/of/dynamic.c:__of_detach_node. The phandle cache > is currently static within drivers/of/base.c. There are a couple of > calls to of_populate_phandle_cache / of_free_phandle_cache within > drivers/of/overlay.c, but these are not involved in the device tree > updates that occur during LPAR migration. A WARN here would only make > sense, if we also arrange to clear the handle. Rob's reply did not include the full patch 2/2. The full patch 2/2 also adds a call to __of_free_phandle_cache_entry() in __of_detach_node(). -Frank > >> >> Rob > > Michael > >> >> >