linux/kernel/trace/trace_events.c, branch v6.17

Merge tag 'trace-v6.17' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

2025-08-01T17:29:36Z

Pull tracing updates from Steven Rostedt: - Deprecate auto-mounting tracefs to /sys/kernel/debug/tracing When tracefs was first introduced back in 2014, the directory /sys/kernel/tracing was added and is the designated location to mount tracefs. To keep backward compatibility, tracefs was auto-mounted in /sys/kernel/debug/tracing as well. All distros now mount tracefs on /sys/kernel/tracing. Having it seen in two different locations has lead to various issues and inconsistencies. The VFS folks have to also maintain debugfs_create_automount() for this single user. It's been over 10 years. Tooling and scripts should start replacing the debugfs location with the tracefs one. The reason tracefs was created in the first place was to allow access to the tracing facilities without the need to configure debugfs into the kernel. Using tracefs should now be more robust. A new config is created: CONFIG_TRACEFS_AUTOMOUNT_DEPRECATED which is default y, so that the kernel is still built with the automount. This config allows those that want to remove the automount from debugfs to do so. When tracefs is accessed from /sys/kernel/debug/tracing, the following printk is triggerd: pr_warn("NOTICE: Automounting of tracing to debugfs is deprecated and will be removed in 2030\n"); This gives users another 5 years to fix their scripts. - Use queue_rcu_work() instead of call_rcu() for freeing event filters The number of filters to be free can be many depending on the number of events within an event system. Freeing them from softirq context can potentially cause undesired latency. Use the RCU workqueue to free them instead. - Remove pointless memory barriers in latency code Memory barriers were added to some of the latency code a long time ago with the idea of "making them visible", but that's not what memory barriers are for. They are to synchronize access between different variables. There was no synchronization here making them pointless. - Remove "__attribute__()" from the type field of event format When LLVM is used to compile the kernel with CONFIG_DEBUG_INFO_BTF=y and PAHOLE_HAS_BTF_TAG=y, some of the format fields get expanded with the following: field:const char * filename; offset:24; size:8; signed:0; Turns into: field:const char __attribute__((btf_type_tag("user"))) * filename; offset:24; size:8; signed:0; This confuses parsers. Add code to strip these tags from the strings. - Add eprobe config option CONFIG_EPROBE_EVENTS Eprobes were added back in 5.15 but were only enabled when another probe was enabled (kprobe, fprobe, uprobe, etc). The eprobes had no config option of their own. Add one as they should be a separate entity. It's default y to keep with the old kernels but still has dependencies on TRACING and HAVE_REGS_AND_STACK_ACCESS_API. - Add eprobe documentation When eprobes were added back in 5.15 no documentation was added to describe them. This needs to be rectified. - Replace open coded cpumask_next_wrap() in move_to_next_cpu() - Have preemptirq_delay_run() use off-stack CPU mask - Remove obsolete comment about pelt_cfs event DECLARE_TRACE() appends "_tp" to trace events now, but the comment above pelt_cfs still mentioned appending it manually. - Remove EVENT_FILE_FL_SOFT_MODE flag The SOFT_MODE flag was required when the soft enabling and disabling of trace events was first introduced. But there was a bug with this approach as it only worked for a single instance. When multiple users required soft disabling and disabling the code was changed to have a ref count. The SOFT_MODE flag is now set iff the ref count is non zero. This is redundant and just reading the ref count is good enough. - Fix typo in comment * tag 'trace-v6.17' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: Documentation: tracing: Add documentation about eprobes tracing: Have eprobes have their own config option tracing: Remove "__attribute__()" from the type field of event format tracing: Deprecate auto-mounting tracefs in debugfs tracing: Fix comment in trace_module_remove_events() tracing: Remove EVENT_FILE_FL_SOFT_MODE flag tracing: Remove pointless memory barriers tracing/sched: Remove obsolete comment on suffixes kernel: trace: preemptirq_delay_test: use offstack cpu mask tracing: Use queue_rcu_work() to free filters tracing: Replace opencoded cpumask_next_wrap() in move_to_next_cpu()

tracing: Remove "attribute()" from the type field of event format

2025-07-29T16:30:41Z

With CONFIG_DEBUG_INFO_BTF=y and PAHOLE_HAS_BTF_TAG=y, `__user` is converted to `__attribute__((btf_type_tag("user")))`. In this case, some syscall events have it for __user data, like below; /sys/kernel/tracing # cat events/syscalls/sys_enter_openat/format name: sys_enter_openat ID: 720 format: field:unsigned short common_type; offset:0; size:2; signed:0; field:unsigned char common_flags; offset:2; size:1; signed:0; field:unsigned char common_preempt_count; offset:3; size:1; signed:0; field:int common_pid; offset:4; size:4; signed:1; field:int __syscall_nr; offset:8; size:4; signed:1; field:int dfd; offset:16; size:8; signed:0; field:const char __attribute__((btf_type_tag("user"))) * filename; offset:24; size:8; signed:0; field:int flags; offset:32; size:8; signed:0; field:umode_t mode; offset:40; size:8; signed:0; Then the trace event filter fails to set the string acceptable flag (FILTER_PTR_STRING) to the field and rejects setting string filter; # echo 'filename.ustring ~ "*ftracetest-dir.wbx24v*"' \ >> events/syscalls/sys_enter_openat/filter sh: write error: Invalid argument # cat error_log [ 723.743637] event filter parse error: error: Expecting numeric field Command: filename.ustring ~ "*ftracetest-dir.wbx24v*" Since this __attribute__ makes format parsing complicated and not needed, remove the __attribute__(.*) from the type string. Cc: Mathieu Desnoyers Link: https://lore.kernel.org/175376583493.1688759.12333973498014733551.stgit@mhiramat.tok.corp.google.com Signed-off-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt (Google)

tracing: Fix comment in trace_module_remove_events()

2025-07-23T00:28:54Z

Fix typo "allocade" -> "allocated". Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Link: https://lore.kernel.org/20250710095628.42ed6b06@batman.local.home Signed-off-by: Steven Rostedt (Google)

tracing: Remove EVENT_FILE_FL_SOFT_MODE flag

2025-07-23T00:15:51Z

When soft disabling of trace events was first created, it needed to have a way to know if a file had a user that was using it with soft disabled (for triggers that need to enable or disable events from a context that can not really enable or disable the event, it would set SOFT_DISABLED to state it is disabled). The flag SOFT_MODE was used to denote that an event had a user that would enable or disable it via the SOFT_DISABLED flag. Commit 1cf4c0732db3c ("tracing: Modify soft-mode only if there's no other referrer") fixed a bug where if two users were using the SOFT_DISABLED flag the accounting would get messed up as the SOFT_MODE flag could only handle one user. That commit added the sm_ref counter which kept track of how many users were using the event in "soft mode". This made the SOFT_MODE flag redundant as it should only be set if the sm_ref counter is non zero. Remove the SOFT_MODE flag and just use the sm_ref counter to know the event is in soft mode or not. This makes the code a bit simpler. Link: https://lore.kernel.org/all/20250702111908.03759998@batman.local.home/ Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Cc: Gabriele Paoloni Link: https://lore.kernel.org/20250702143657.18dd1882@batman.local.home Signed-off-by: Steven Rostedt (Google)

tracing: Add down_write(trace_event_sem) when adding trace event

2025-07-19T17:54:59Z

When a module is loaded, it adds trace events defined by the module. It may also need to modify the modules trace printk formats to replace enum names with their values. If two modules are loaded at the same time, the adding of the event to the ftrace_events list can corrupt the walking of the list in the code that is modifying the printk format strings and crash the kernel. The addition of the event should take the trace_event_sem for write while it adds the new event. Also add a lockdep_assert_held() on that semaphore in __trace_add_event_dirs() as it iterates the list. Cc: stable@vger.kernel.org Cc: Mathieu Desnoyers Acked-by: Masami Hiramatsu (Google) Link: https://lore.kernel.org/20250718223158.799bfc0c@batman.local.home Reported-by: Fusheng Huang(黄富生) Closes: https://lore.kernel.org/all/20250717105007.46ccd18f@batman.local.home/ Fixes: 110bf2b764eb6 ("tracing: add protection around module events unload") Signed-off-by: Steven Rostedt (Google)

tracing: Add a helper function to handle the dereference arg in verifier

2025-05-09T19:19:11Z

Add a helper function called handle_dereference_arg() to replace the logic that is identical in two locations of test_event_printk(). Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Link: https://lore.kernel.org/20250507191703.5dd8a61d@gandalf.local.home Signed-off-by: Steven Rostedt (Google)

tracing: Just use this_cpu_read() to access ignore_pid

2025-05-08T13:36:09Z

The ignore_pid boolean on the per CPU data descriptor is updated at sched_switch when a new task is scheduled in. If the new task is to be ignored, it is set to true, otherwise it is set to false. The current task should always have the correct value as it is updated when the task is scheduled in. Instead of breaking up the read of this value, which requires preemption to be disabled, just use this_cpu_read() which gives a snapshot of the value. Since the value will always be correct for a given task (because it's updated at sched switch) it doesn't need preemption disabled. This will also allow trace events to be called with preemption enabled. Cc: Masami Hiramatsu Cc: Mark Rutland Cc: Mathieu Desnoyers Cc: Andrew Morton Link: https://lore.kernel.org/20250505212235.038958766@goodmis.org Signed-off-by: Steven Rostedt (Google)

tracing: Verify event formats that have "%*p.."

2025-04-02T13:51:26Z

The trace event verifier checks the formats of trace events to make sure that they do not point at memory that is not in the trace event itself or in data that will never be freed. If an event references data that was allocated when the event triggered and that same data is freed before the event is read, then the kernel can crash by reading freed memory. The verifier runs at boot up (or module load) and scans the print formats of the events and checks their arguments to make sure that dereferenced pointers are safe. If the format uses "%*p.." the verifier will ignore it, and that could be dangerous. Cover this case as well. Also add to the sample code a use case of "%*pbl". Link: https://lore.kernel.org/all/bcba4d76-2c3f-4d11-baf0-02905db953dd@oracle.com/ Cc: stable@vger.kernel.org Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Fixes: 5013f454a352c ("tracing: Add check of trace event print fmts for dereferencing pointers") Link: https://lore.kernel.org/20250327195311.2d89ec66@gandalf.local.home Reported-by: Libo Chen Reviewed-by: Libo Chen Tested-by: Libo Chen Signed-off-by: Steven Rostedt (Google)

Merge tag 'trace-ringbuffer-v6.15-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

2025-03-31T20:37:22Z

Pull ring-buffer updates from Steven Rostedt: - Restructure the persistent memory to have a "scratch" area Instead of hard coding the KASLR offset in the persistent memory by the ring buffer, push that work up to the callers of the persistent memory as they are the ones that need this information. The offsets and such is not important to the ring buffer logic and it should not be part of that. A scratch pad is now created when the caller allocates a ring buffer from persistent memory by stating how much memory it needs to save. - Allow where modules are loaded to be saved in the new scratch pad Save the addresses of modules when they are loaded into the persistent memory scratch pad. - A new module_for_each_mod() helper function was created With the acknowledgement of the module maintainers a new module helper function was created to iterate over all the currently loaded modules. This has a callback to be called for each module. This is needed for when tracing is started in the persistent buffer and the currently loaded modules need to be saved in the scratch area. - Expose the last boot information where the kernel and modules were loaded The last_boot_info file is updated to print out the addresses of where the kernel "_text" location was loaded from a previous boot, as well as where the modules are loaded. If the buffer is recording the current boot, it only prints "# Current" so that it does not expose the KASLR offset of the currently running kernel. - Allow the persistent ring buffer to be released (freed) To have this in production environments, where the kernel command line can not be changed easily, the ring buffer needs to be freed when it is not going to be used. The memory for the buffer will always be allocated at boot up, but if the system isn't going to enable tracing, the memory needs to be freed. Allow it to be freed and added back to the kernel memory pool. - Allow stack traces to print the function names in the persistent buffer Now that the modules are saved in the persistent ring buffer, if the same modules are loaded, the printing of the function names will examine the saved modules. If the module is found in the scratch area and is also loaded, then it will do the offset shift and use kallsyms to display the function name. If the address is not found, it simply displays the address from the previous boot in hex. * tag 'trace-ringbuffer-v6.15-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: tracing: Use _text and the kernel offset in last_boot_info tracing: Show last module text symbols in the stacktrace ring-buffer: Remove the unused variable bmeta tracing: Skip update_last_data() if cleared and remove active check for save_mod() tracing: Initialize scratch_size to zero to prevent UB tracing: Fix a compilation error without CONFIG_MODULES tracing: Freeable reserved ring buffer mm/memblock: Add reserved memory release function tracing: Update modules to persistent instances when loaded tracing: Show module names and addresses of last boot tracing: Have persistent trace instances save module addresses module: Add module_for_each_mod() function tracing: Have persistent trace instances save KASLR offset ring-buffer: Add ring_buffer_meta_scratch() ring-buffer: Add buffer meta data for persistent ring buffer ring-buffer: Use kaslr address instead of text delta ring-buffer: Fix bytes_dropped calculation issue

tracing: Update modules to persistent instances when loaded

2025-03-28T12:39:27Z

When a module is loaded and a persistent buffer is actively tracing, add it to the list of modules in the persistent memory. Cc: Masami Hiramatsu Cc: Mark Rutland Cc: Mathieu Desnoyers Cc: Andrew Morton Link: https://lore.kernel.org/20250305164609.469844721@goodmis.org Signed-off-by: Steven Rostedt (Google)