From 034dd340b08be1f2f0477ad16131d609f9dbd53c Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sun, 30 Aug 2026 09:22:00 -0700 Subject: Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace Pull tracing fixes from Steven Rostedt: - Fix error output of boot instance creation failure Currently if a boot instance creation fails, instead of printing out the name of the instance that failed, it prints "(null)". That is because it prints "cur_str" that had already been processed by strsep(). Print the saved name instead. While at it, print the error code of the failure. - Fix use-after-free for same named historgrams Histograms can be named so that they can be used in multiple events. But if the named histogram has a variable attached, the second event that uses the named histogram which duplicates it and needs to free the original after duplication leaves the old variable in place and still visible. If another histogram uses than variable, it will use the stale one which will try to reference the freed duplicate histogram and crash the kernel. Free the duplicate variables along with the duplicated histogram data. - Check return value of kthread_run() in event self test The events self tests uses a kthread for testing but does not check if it succeeded in creating a kthread. If the kthread creation were to fail, the code will still try to call kthread_stop() on the error returned. - Fix race between reading trace_pipe and updating subbuffer size If a user is reading the trace_pipe file at the same time they update the ring buffer sub-buffer size, can cause the trace_pipe read to read stale data. Add trace_access_lock() around updating the ring buffer sub-buffer size. - Fix eventfs_inode on failure path in creation of the events directory In the creation of the "events" directory, if after allocating the eventfs_inode a failure is detected, it calls cleanup_ei() which calls free_ei(). The free_ei() will test if eventfs_inode being freed has no children. It is a bug if it does. But on the failure case of the creation of the "events" directory, the children lists have not yet been initialized and the free will trigger a warning because list_empty() on an uninitialized list returns false. Move the initialization into init_ei() where it makes more sense and makes sure that a created eventfs_inode has its lists initialized upon creation. - Check return value of kthread_run() in ftrace direct sample code The sample code that shows how to use the ftrace direct calls does not test the return of kthread_run() to see if it succeeds. Return a failure if the kthread_run() doesn't succeed. - Clear user events state on fork in case of alloc failure On fork, the child gets a pointer to the parent's user events state. It makes a copy of it then updates the child's pointer to it. But if the allocation fails, the duplication function leaves the child with a pointer to its parent's descriptor. When the child cleans up its data, it will free the parent's descriptor while the parent is still using it. In the duplication function, set the child's user_event_mm to NULL before testing if the allocation succeeded, and when it exits it will not free the parent's descriptor. - Fix retry exhaustion in simple ring buffer reader swap simple_ring_buffer_swap_reader_page() starts with retry set to 8 and post-decrements it only after a failed link replacement. On the final attempt, a successful replacement leaves retry at zero, while a failed replacement leaves it at -1. But the check for success expects the retry value to be non-zero and exits with an error on zero. This is the opposite result. Fix it. - Fail nicely when the remote swap_reader_page() returns an error Currently, if the swap_reader_page() of a remote buffer fails, it triggers a WARN_ON_ONCE() and continues normally. Instead, have it exit with an error and a pr_warn() print instead of a full WARNING. * tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: ring-buffer: Stop remote reader update when page swap fails tracing: Fix retry exhaustion in simple ring buffer reader swap tracing/user_events: Clear copied tracing state before fork duplication samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify eventfs: Initialize ei->children and ei->list in init_ei() tracing: Fix use-after-free in trace_pipe read on sub-buffer order change tracing: Fix crash passing ERR_PTR to kthread_stop() tracing: Fix use-after-free with same-name named triggers tracing: Fix logged instance name on creation failure --- .../arch/arm/google/chromebook-boot-flow.rst | 69 ++++++++++++++++++++++ 1 file changed, 69 insertions(+) create mode 100644 Documentation/arch/arm/google/chromebook-boot-flow.rst (limited to 'Documentation/arch/arm/google') diff --git a/Documentation/arch/arm/google/chromebook-boot-flow.rst b/Documentation/arch/arm/google/chromebook-boot-flow.rst new file mode 100644 index 000000000..36da77684 --- /dev/null +++ b/Documentation/arch/arm/google/chromebook-boot-flow.rst @@ -0,0 +1,69 @@ +.. SPDX-License-Identifier: GPL-2.0 + +====================================== +Chromebook Boot Flow +====================================== + +Most recent Chromebooks that use device tree are using the opensource +depthcharge_ bootloader. Depthcharge_ expects the OS to be packaged as a `FIT +Image`_ which contains an OS image as well as a collection of device trees. It +is up to depthcharge_ to pick the right device tree from the `FIT Image`_ and +provide it to the OS. + +The scheme that depthcharge_ uses to pick the device tree takes into account +three variables: + +- Board name, specified at depthcharge_ compile time. This is $(BOARD) below. +- Board revision number, determined at runtime (perhaps by reading GPIO + strappings, perhaps via some other method). This is $(REV) below. +- SKU number, read from GPIO strappings at boot time. This is $(SKU) below. + +For recent Chromebooks, depthcharge_ creates a match list that looks like this: + +- google,$(BOARD)-rev$(REV)-sku$(SKU) +- google,$(BOARD)-rev$(REV) +- google,$(BOARD)-sku$(SKU) +- google,$(BOARD) + +Note that some older Chromebooks use a slightly different list that may +not include SKU matching or may prioritize SKU/rev differently. + +Note that for some boards there may be extra board-specific logic to inject +extra compatibles into the list, but this is uncommon. + +Depthcharge_ will look through all device trees in the `FIT Image`_ trying to +find one that matches the most specific compatible. It will then look +through all device trees in the `FIT Image`_ trying to find the one that +matches the *second most* specific compatible, etc. + +When searching for a device tree, depthcharge_ doesn't care where the +compatible string falls within a device tree's root compatible string array. +As an example, if we're on board "lazor", rev 4, SKU 0 and we have two device +trees: + +- "google,lazor-rev5-sku0", "google,lazor-rev4-sku0", "qcom,sc7180" +- "google,lazor", "qcom,sc7180" + +Then depthcharge_ will pick the first device tree even though +"google,lazor-rev4-sku0" was the second compatible listed in that device tree. +This is because it is a more specific compatible than "google,lazor". + +It should be noted that depthcharge_ does not have any smarts to try to +match board or SKU revisions that are "close by". That is to say that +if depthcharge_ knows it's on "rev4" of a board but there is no "rev4" +device tree then depthcharge_ *won't* look for a "rev3" device tree. + +In general when any significant changes are made to a board the board +revision number is increased even if none of those changes need to +be reflected in the device tree. Thus it's fairly common to see device +trees with multiple revisions. + +It should be noted that, taking into account the above system that +depthcharge_ has, the most flexibility is achieved if the device tree +supporting the newest revision(s) of a board omits the "-rev{REV}" +compatible strings. When this is done then if you get a new board +revision and try to run old software on it then we'll at pick the +newest device tree we know about. + +.. _depthcharge: https://source.chromium.org/chromiumos/chromiumos/codesearch/+/main:src/platform/depthcharge/ +.. _`FIT Image`: https://doc.coreboot.org/lib/payloads/fit.html -- cgit v1.3.1