user/sven/linux.git/kernel/trace/ring_buffer.c, branch v6.15.1

ring-buffer: Fix persistent buffer when commit page is the reader page

2025-05-14T17:53:23Z

The ring buffer is made up of sub buffers (sometimes called pages as they are by default PAGE_SIZE). It has the following "pages": "tail page" - this is the page that the next write will write to "head page" - this is the page that the reader will swap the reader page with. "reader page" - This belongs to the reader, where it will swap the head page from the ring buffer so that the reader does not race with the writer. The writer may end up on the "reader page" if the ring buffer hasn't written more than one page, where the "tail page" and the "head page" are the same. The persistent ring buffer has meta data that points to where these pages exist so on reboot it can re-create the pointers to the cpu_buffer descriptor. But when the commit page is on the reader page, the logic is incorrect. The check to see if the commit page is on the reader page checked if the head page was the reader page, which would never happen, as the head page is always in the ring buffer. The correct check would be to test if the commit page is on the reader page. If that's the case, then it can exit out early as the commit page is only on the reader page when there's only one page of data in the buffer. There's no reason to iterate the ring buffer pages to find the "commit page" as it is already found. To trigger this bug: # echo 1 > /sys/kernel/tracing/instances/boot_mapped/events/syscalls/sys_enter_fchownat/enable # touch /tmp/x # chown sshd /tmp/x # reboot On boot up, the dmesg will have: Ring buffer meta [0] is from previous boot! Ring buffer meta [1] is from previous boot! Ring buffer meta [2] is from previous boot! Ring buffer meta [3] is from previous boot! Ring buffer meta [4] commit page not found Ring buffer meta [5] is from previous boot! Ring buffer meta [6] is from previous boot! Ring buffer meta [7] is from previous boot! Where the buffer on CPU 4 had a "commit page not found" error and that buffer is cleared and reset causing the output to be empty and the data lost. When it works correctly, it has: # cat /sys/kernel/tracing/instances/boot_mapped/trace_pipe <...>-1137 [004] ..... 998.205323: sys_enter_fchownat: __syscall_nr=0x104 (260) dfd=0xffffff9c (4294967196) filename=(0xffffc90000a0002c) user=0x3e8 (1000) group=0xffffffff (4294967295) flag=0x0 (0 Cc: stable@vger.kernel.org Cc: Mathieu Desnoyers Link: https://lore.kernel.org/20250513115032.3e0b97f7@gandalf.local.home Fixes: 5f3b6e839f3ce ("ring-buffer: Validate boot range memory events") Reported-by: Tasos Sahanidis Tested-by: Tasos Sahanidis Reviewed-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt (Google)

Merge tag 'trace-ringbuffer-v6.15-3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

2025-04-03T23:09:29Z

Pull ring-buffer updates from Steven Rostedt: "Persistent buffer cleanups and simplifications. It was mistaken that the physical memory returned from "reserve_mem" had to be vmap()'d to get to it from a virtual address. But reserve_mem already maps the memory to the virtual address of the kernel so a simple phys_to_virt() can be used to get to the virtual address from the physical memory returned by "reserve_mem". With this new found knowledge, the code can be cleaned up and simplified. - Enforce that the persistent memory is page aligned As the buffers using the persistent memory are all going to be mapped via pages, make sure that the memory given to the tracing infrastructure is page aligned. If it is not, it will print a warning and fail to map the buffer. - Use phys_to_virt() to get the virtual address from reserve_mem Instead of calling vmap() on the physical memory returned from "reserve_mem", use phys_to_virt() instead. As the memory returned by "memmap" or any other means where a physical address is given to the tracing infrastructure, it still needs to be vmap(). Since this memory can never be returned back to the buddy allocator nor should it ever be memmory mapped to user space, flag this buffer and up the ref count. The ref count will keep it from ever being freed, and the flag will prevent it from ever being memory mapped to user space. - Use vmap_page_range() for memmap virtual address mapping For the memmap buffer, instead of allocating an array of struct pages, assigning them to the contiguous phsycial memory and then passing that to vmap(), use vmap_page_range() instead - Replace flush_dcache_folio() with flush_kernel_vmap_range() Instead of calling virt_to_folio() and passing that to flush_dcache_folio(), just call flush_kernel_vmap_range() directly. This also fixes a bug where if a subbuffer was bigger than PAGE_SIZE only the PAGE_SIZE portion would be flushed" * tag 'trace-ringbuffer-v6.15-3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: ring-buffer: Use flush_kernel_vmap_range() over flush_dcache_folio() tracing: Use vmap_page_range() to map memmap ring buffer tracing: Have reserve_mem use phys_to_virt() and separate from memmap buffer tracing: Enforce the persistent ring buffer to be page aligned

ring-buffer: Use flush_kernel_vmap_range() over flush_dcache_folio()

2025-04-02T15:02:27Z

Some architectures do not have data cache coherency between user and kernel space. For these architectures, the cache needs to be flushed on both the kernel and user addresses so that user space can see the updates the kernel has made. Instead of using flush_dcache_folio() and playing with virt_to_folio() within the call to that function, use flush_kernel_vmap_range() which takes the virtual address and does the work for those architectures that need it. This also fixes a bug where the flush of the reader page only flushed one page. If the sub-buffer order is 1 or more, where the sub-buffer size would be greater than a page, it would miss the rest of the sub-buffer content, as the "reader page" is not just a page, but the size of a sub-buffer. Link: https://lore.kernel.org/all/CAG48ez3w0my4Rwttbc5tEbNsme6tc0mrSN95thjXUFaJ3aQ6SA@mail.gmail.com/ Cc: stable@vger.kernel.org Cc: Linus Torvalds Cc: Masami Hiramatsu Cc: Mark Rutland Cc: Mathieu Desnoyers Cc: Andrew Morton Cc: Vincent Donnefort Cc: Vlastimil Babka Cc: Mike Rapoport Link: https://lore.kernel.org/20250402144953.920792197@goodmis.org Fixes: 117c39200d9d7 ("ring-buffer: Introducing ring-buffer mapping functions"); Suggested-by: Jann Horn 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

ring-buffer: Remove the unused variable bmeta

2025-03-28T12:39:56Z

Variable bmeta is not effectively used, so delete it. kernel/trace/ring_buffer.c:1952:27: warning: variable ‘bmeta’ set but not used. Link: https://lore.kernel.org/20250317015524.3902-1-jiapeng.chong@linux.alibaba.com Reported-by: Abaci Robot Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=19524 Signed-off-by: Jiapeng Chong Signed-off-by: Steven Rostedt (Google)

tracing: Have persistent trace instances save KASLR offset

2025-03-28T12:39:27Z

There's no reason to save the KASLR offset for the ring buffer itself. That is used by the tracer. Now that the tracer has a way to save data in the persistent memory of the ring buffer, have the tracing infrastructure take care of the saving of the KASLR offset. Cc: Mark Rutland Cc: Mathieu Desnoyers Cc: Andrew Morton Link: https://lore.kernel.org/20250305164608.792722274@goodmis.org Reviewed-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt (Google)

ring-buffer: Add ring_buffer_meta_scratch()

2025-03-28T12:39:27Z

Now that there's one meta data at the start of the persistent memory used by the ring buffer, allow the caller to request some memory right after that data that it can use as its own persistent memory. Also fix some white space issues with ring_buffer_alloc(). Cc: Mark Rutland Cc: Mathieu Desnoyers Cc: Andrew Morton Link: https://lore.kernel.org/20250305164608.619631731@goodmis.org Reviewed-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt (Google)

ring-buffer: Add buffer meta data for persistent ring buffer

2025-03-28T12:39:26Z

Instead of just having a meta data at the first page of each sub buffer that has duplicate data, add a new meta page to the entire block of memory that holds the duplicate data and remove it from the sub buffer meta data. This will open up the extra memory in this first page to be used by the tracer for its own persistent data. Cc: Mark Rutland Cc: Mathieu Desnoyers Cc: Andrew Morton Link: https://lore.kernel.org/20250305164608.446351513@goodmis.org Reviewed-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt (Google)

ring-buffer: Use kaslr address instead of text delta

2025-03-28T12:39:26Z

Instead of saving off the text and data pointers and using them to compare with the current boot's text and data pointers, just save off the KASLR offset. Then that can be used to figure out how to read the previous boots buffer. The last_boot_info will now show this offset, but only if it is for a previous boot: ~# cat instances/boot_mapped/last_boot_info 39000000 [kernel] ~# echo function > instances/boot_mapped/current_tracer ~# cat instances/boot_mapped/last_boot_info # Current If the KASLR offset saved is for the current boot, the last_boot_info will show the value of "current". Cc: Mark Rutland Cc: Mathieu Desnoyers Cc: Andrew Morton Link: https://lore.kernel.org/20250305164608.274956504@goodmis.org Reviewed-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt (Google)

ring-buffer: Fix bytes_dropped calculation issue

2025-03-28T12:39:26Z

The calculation of bytes-dropped and bytes_dropped_nested is reversed. Although it does not affect the final calculation of total_dropped, it should still be modified. Link: https://lore.kernel.org/20250223070106.6781-1-yangfeng59949@163.com Fixes: 6c43e554a2a5 ("ring-buffer: Add ring buffer startup selftest") Signed-off-by: Feng Yang Signed-off-by: Steven Rostedt (Google)