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Wed, 30 Sep 2026 00:18:23 -0700 (PDT) Date: Wed, 30 Sep 2026 15:18:19 +0800 From: Yonghao Zhang To: Mathieu Poirier Cc: andersson@kernel.org, linux-remoteproc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] remoteproc: core: Fetch the auto-boot firmware only once Message-ID: <20260930071819.vse5i32snb744ay7@embedsky001.tail6d6b2f.ts.net> References: <20260923025855.2523147-1-hyz3367@gmail.com> <20260929044312.kkqnizsdtg2axg7c@embedsky001.tail6d6b2f.ts.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Sep 29, 2026 at 09:06:35AM -0600, Mathieu Poirier wrote: > On Mon, 28 Sept 2026 at 22:43, Yonghao Zhang wrote: > > > > Hi Mathieu, > > > > Thanks for the review. > > > > On Mon, Sep 28, 2026 at 11:34:14AM -0600, Mathieu Poirier wrote: > > > Good day, > > > > > > On Wed, Sep 23, 2026 at 10:58:55AM +0800, Yonghao Zhang wrote: > > > > Auto-boot for an always-on remote processor registers an asynchronous > > > > request_firmware_nowait() whose callback discards the fetched image > > > > > > The callback function is rproc_auto_boot_callback() but I don't see where the > > > image fetched by request_firmware_nowait() is discarded. > > > > It is the release_firmware(fw) called at the end of this callback. > > Right, this is happening at the _end_ of the callback, but the > changelog says the firmware is discarded and then rproc_boot() called. > This is not accurate and needs to be fixed. > The [PATCH v2] I sent earlier today carries a wrong In-Reply-To and won't show up in this thread on lore. It is available here: https://lore.kernel.org/linux-remoteproc/20260930064144.645211-1-hyz3367@gmail.com/T/#u Thanks, Yonghao > > The image fetched by request_firmware_nowait() is never consumed: > > rproc_boot() doesn't take it as an argument and fetches it's own copy > > with a synchronous request_firmware(). It is that second copy which > > rproc_fw_boot() parses and which is release at the end of rproc_boot(). > > The asynchronous copy is only ever touched by the final > > release_firmware(fw) -- fetched, never read, freed. > > > > "Discarded" in the commit message refers to exactly that. I can send > > a v2 that names this release_firmware() explicitly in the first > > paragraph if you want the message to be verifiable at a glance. > > > > Thanks, > > Yonghao > > > > > > > > Otherwise I agree with this patch. > > > > > > Thanks, > > > Mathieu > > > > > > > and calls rproc_boot(). rproc_boot() then fetches the very same image > > > > again with a synchronous request_firmware(), so every auto-boot reads > > > > the firmware image twice and allocates the buffer twice; on kernels > > > > with the sysfs fallback enabled, the uevent round-trip is repeated > > > > as well. > > > > > > > > The asynchronous request exists only so that rproc_add() does not > > > > block on the filesystem read; the image it fetches is never used. > > > > The core already defers rproc_boot() to a worker for detached > > > > processors (attach_work). Reuse that worker for offline processors > > > > too and drop the asynchronous firmware request: rproc_boot() fetches > > > > the image exactly once and dispatches between a firmware boot and > > > > an attach based on the proccessor state. The work is renamed to > > > > boot_work to match its widened role. > > > > > > > > commit 400e64df6b23 ("remoteproc: add framework for controlling remote > > > > processors") noted back in 2011 that "we must wait until it completes > > > > before we try to unregister the device". rproc_del() now does exactly > > > > that: it waits for the boot work with cancel_work_sync(), which also > > > > closes the theoretical window in which a pending attach work could > > > > outlive the rproc instance. > > > > > > > > The changed fallback behaviour only matters for legacy > > > > configurations. udev dropped its userspace firmware loader back in > > > > 2014, as recorded in > > > > Documentation/driver-api/firmware/fallback-mechanisms.rst, and the > > > > kernel has documented since commit 02c399306826 ("firmware_loader: > > > > enhance Kconfig documentation over FW_LOADER") that "Linux no longer > > > > relies on or uses a fallback mechanism in userspace". Auto-boot now > > > > uses the same synchronous fallback semantics as every other explicit > > > > boot source (sysfs, cdev). > > > > > > > > Signed-off-by: Yonghao Zhang > > > > --- > > > > drivers/remoteproc/remoteproc_core.c | 65 ++++++++-------------------- > > > > include/linux/remoteproc.h | 4 +- > > > > 2 files changed, 21 insertions(+), 48 deletions(-) > > > > > > > > diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c > > > > index 263e12f022ea..f329dc478170 100644 > > > > --- a/drivers/remoteproc/remoteproc_core.c > > > > +++ b/drivers/remoteproc/remoteproc_core.c > > > > @@ -1662,49 +1662,26 @@ static int rproc_attach(struct rproc *rproc) > > > > } > > > > > > > > /* > > > > - * take a firmware and boot it up. > > > > - * > > > > - * Note: this function is called asynchronously upon registration of the > > > > - * remote processor (so we must wait until it completes before we try > > > > - * to unregister the device. one other option is just to use kref here, > > > > - * that might be cleaner). > > > > + * Boot or attach the remote processor in the background, on behalf of > > > > + * rproc_trigger_auto_boot(): rproc_add() runs in probe context and must > > > > + * not block while the firmware image is read from storage. rproc_boot() > > > > + * dispatches on the processor state, so this covers both a firmware boot > > > > + * and an attach to a processor started by another entity. > > > > + * > > > > + * Note: rproc_del() waits for this work to complete with > > > > + * cancel_work_sync(), so the rproc instance remains valid for the > > > > + * entire lifetime of this function. > > > > */ > > > > -static void rproc_auto_boot_callback(const struct firmware *fw, void *context) > > > > +static void rproc_boot_work(struct work_struct *work) > > > > { > > > > - struct rproc *rproc = context; > > > > + struct rproc *rproc = container_of(work, struct rproc, boot_work); > > > > > > > > rproc_boot(rproc); > > > > - > > > > - release_firmware(fw); > > > > } > > > > > > > > -static void rproc_attach_work(struct work_struct *work) > > > > +static void rproc_trigger_auto_boot(struct rproc *rproc) > > > > { > > > > - struct rproc *rproc = container_of(work, struct rproc, attach_work); > > > > - > > > > - rproc_boot(rproc); > > > > -} > > > > - > > > > -static int rproc_trigger_auto_boot(struct rproc *rproc) > > > > -{ > > > > - int ret; > > > > - > > > > - if (rproc->state == RPROC_DETACHED) { > > > > - schedule_work(&rproc->attach_work); > > > > - return 0; > > > > - } > > > > - > > > > - /* > > > > - * We're initiating an asynchronous firmware loading, so we can > > > > - * be built-in kernel code, without hanging the boot process. > > > > - */ > > > > - ret = request_firmware_nowait(THIS_MODULE, FW_ACTION_UEVENT, > > > > - rproc->firmware, &rproc->dev, GFP_KERNEL, > > > > - rproc, rproc_auto_boot_callback); > > > > - if (ret < 0) > > > > - dev_err(&rproc->dev, "request_firmware_nowait err: %d\n", ret); > > > > - > > > > - return ret; > > > > + schedule_work(&rproc->boot_work); > > > > } > > > > > > > > static int rproc_stop(struct rproc *rproc, bool crashed) > > > > @@ -2348,11 +2325,8 @@ int rproc_add(struct rproc *rproc) > > > > rproc_create_debug_dir(rproc); > > > > > > > > /* if rproc is marked always-on, request it to boot */ > > > > - if (rproc->auto_boot) { > > > > - ret = rproc_trigger_auto_boot(rproc); > > > > - if (ret < 0) > > > > - goto rproc_remove_dev; > > > > - } > > > > + if (rproc->auto_boot) > > > > + rproc_trigger_auto_boot(rproc); > > > > > > > > /* expose to rproc_get_by_phandle users */ > > > > mutex_lock(&rproc_list_mutex); > > > > @@ -2361,10 +2335,6 @@ int rproc_add(struct rproc *rproc) > > > > > > > > return 0; > > > > > > > > -rproc_remove_dev: > > > > - cancel_work_sync(&rproc->crash_handler); > > > > - rproc_delete_debug_dir(rproc); > > > > - device_del(dev); > > > > rproc_remove_cdev: > > > > rproc_char_device_remove(rproc); > > > > return ret; > > > > @@ -2552,7 +2522,7 @@ struct rproc *rproc_alloc(struct device *dev, const char *name, > > > > INIT_LIST_HEAD(&rproc->subdevs); > > > > INIT_LIST_HEAD(&rproc->dump_segments); > > > > > > > > - INIT_WORK(&rproc->attach_work, rproc_attach_work); > > > > + INIT_WORK(&rproc->boot_work, rproc_boot_work); > > > > INIT_WORK(&rproc->crash_handler, rproc_crash_handler_work); > > > > spin_lock_init(&rproc->crash_handler_lock); > > > > > > > > @@ -2630,6 +2600,9 @@ int rproc_del(struct rproc *rproc) > > > > if (cancel_work_sync(&rproc->crash_handler)) > > > > pm_relax(rproc->dev.parent); > > > > > > > > + /* auto-boot may still be fetching firmware: wait for it here */ > > > > + cancel_work_sync(&rproc->boot_work); > > > > + > > > > __rproc_shutdown(rproc, true); > > > > > > > > rproc_delete_debug_dir(rproc); > > > > diff --git a/include/linux/remoteproc.h b/include/linux/remoteproc.h > > > > index a44368737b39..d77e24539133 100644 > > > > --- a/include/linux/remoteproc.h > > > > +++ b/include/linux/remoteproc.h > > > > @@ -231,7 +231,7 @@ enum rproc_features { > > > > * @subdevs: list of subdevices, to following the running state > > > > * @notifyids: idr for dynamically assigning rproc-wide unique notify ids > > > > * @index: index of this rproc device > > > > - * @attach_work: workqueue for attaching rproc > > > > + * @boot_work: workqueue for booting rproc > > > > * @crash_handler: workqueue for handling a crash > > > > * @crash_handler_lock: serializes crash handler queueing and deletion > > > > * @deleting: remoteproc deletion has begun > > > > @@ -277,7 +277,7 @@ struct rproc { > > > > struct list_head subdevs; > > > > struct idr notifyids; > > > > int index; > > > > - struct work_struct attach_work; > > > > + struct work_struct boot_work; > > > > struct work_struct crash_handler; > > > > spinlock_t crash_handler_lock; > > > > bool deleting; > > > > -- > > > > 2.34.1 > > > >