linux/kernel/trace, branch v6.8

Merge tag 'trace-ring-buffer-v6.8-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

2024-03-10T18:53:21Z

Pull tracing fixes from Steven Rostedt: - Do not allow large strings (> 4096) as single write to trace_marker The size of a string written into trace_marker was determined by the size of the sub-buffer in the ring buffer. That size is dependent on the PAGE_SIZE of the architecture as it can be mapped into user space. But on PowerPC, where PAGE_SIZE is 64K, that made the limit of the string of writing into trace_marker 64K. One of the selftests looks at the size of the ring buffer sub-buffers and writes that plus more into the trace_marker. The write will take what it can and report back what it consumed so that the user space application (like echo) will write the rest of the string. The string is stored in the ring buffer and can be read via the "trace" or "trace_pipe" files. The reading of the ring buffer uses vsnprintf(), which uses a precision "%.*s" to make sure it only reads what is stored in the buffer, as a bug could cause the string to be non terminated. With the combination of the precision change and the PAGE_SIZE of 64K allowing huge strings to be added into the ring buffer, plus the test that would actually stress that limit, a bug was reported that the precision used was too big for "%.*s" as the string was close to 64K in size and the max precision of vsnprintf is 32K. Linus suggested not to have that precision as it could hide a bug if the string was again stored without a nul byte. Another issue that was brought up is that the trace_seq buffer is also based on PAGE_SIZE even though it is not tied to the architecture limit like the ring buffer sub-buffer is. Having it be 64K * 2 is simply just too big and wasting memory on systems with 64K page sizes. It is now hardcoded to 8K which is what all other architectures with 4K PAGE_SIZE has. Finally, the write to trace_marker is now limited to 4K as there is no reason to write larger strings into trace_marker. - ring_buffer_wait() should not loop. The ring_buffer_wait() does not have the full context (yet) on if it should loop or not. Just exit the loop as soon as its woken up and let the callers decide to loop or not (they already do, so it's a bit redundant). - Fix shortest_full field to be the smallest amount in the ring buffer that a waiter is waiting for. The "shortest_full" field is updated when a new waiter comes in and wants to wait for a smaller amount of data in the ring buffer than other waiters. But after all waiters are woken up, it's not reset, so if another waiter comes in wanting to wait for more data, it will be woken up when the ring buffer has a smaller amount from what the previous waiters were waiting for. - The wake up all waiters on close is incorrectly called frome .release() and not from .flush() so it will never wake up any waiters as the .release() will not get called until all .read() calls are finished. And the wakeup is for the waiters in those .read() calls. * tag 'trace-ring-buffer-v6.8-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: tracing: Use .flush() call to wake up readers ring-buffer: Fix resetting of shortest_full ring-buffer: Fix waking up ring buffer readers tracing: Limit trace_marker writes to just 4K tracing: Limit trace_seq size to just 8K and not depend on architecture PAGE_SIZE tracing: Remove precision vsnprintf() check from print event

tracing: Use .flush() call to wake up readers

2024-03-10T16:27:47Z

The .release() function does not get called until all readers of a file descriptor are finished. If a thread is blocked on reading a file descriptor in ring_buffer_wait(), and another thread closes the file descriptor, it will not wake up the other thread as ring_buffer_wake_waiters() is called by .release(), and that will not get called until the .read() is finished. The issue originally showed up in trace-cmd, but the readers are actually other processes with their own file descriptors. So calling close() would wake up the other tasks because they are blocked on another descriptor then the one that was closed(). But there's other wake ups that solve that issue. When a thread is blocked on a read, it can still hang even when another thread closed its descriptor. This is what the .flush() callback is for. Have the .flush() wake up the readers. Link: https://lore.kernel.org/linux-trace-kernel/20240308202432.107909457@goodmis.org Cc: stable@vger.kernel.org Cc: Masami Hiramatsu Cc: Mark Rutland Cc: Mathieu Desnoyers Cc: Andrew Morton Cc: Linus Torvalds Cc: linke li Cc: Rabin Vincent Fixes: f3ddb74ad0790 ("tracing: Wake up ring buffer waiters on closing of the file") Signed-off-by: Steven Rostedt (Google)

ring-buffer: Fix resetting of shortest_full

2024-03-10T16:27:40Z

The "shortest_full" variable is used to keep track of the waiter that is waiting for the smallest amount on the ring buffer before being woken up. When a tasks waits on the ring buffer, it passes in a "full" value that is a percentage. 0 means wake up on any data. 1-100 means wake up from 1% to 100% full buffer. As all waiters are on the same wait queue, the wake up happens for the waiter with the smallest percentage. The problem is that the smallest_full on the cpu_buffer that stores the smallest amount doesn't get reset when all the waiters are woken up. It does get reset when the ring buffer is reset (echo > /sys/kernel/tracing/trace). This means that tasks may be woken up more often then when they want to be. Instead, have the shortest_full field get reset just before waking up all the tasks. If the tasks wait again, they will update the shortest_full before sleeping. Also add locking around setting of shortest_full in the poll logic, and change "work" to "rbwork" to match the variable name for rb_irq_work structures that are used in other places. Link: https://lore.kernel.org/linux-trace-kernel/20240308202431.948914369@goodmis.org Cc: stable@vger.kernel.org Cc: Masami Hiramatsu Cc: Mark Rutland Cc: Mathieu Desnoyers Cc: Andrew Morton Cc: Linus Torvalds Cc: linke li Cc: Rabin Vincent Fixes: 2c2b0a78b3739 ("ring-buffer: Add percentage of ring buffer full to wake up reader") Signed-off-by: Steven Rostedt (Google)

ring-buffer: Fix waking up ring buffer readers

2024-03-10T16:24:59Z

A task can wait on a ring buffer for when it fills up to a specific watermark. The writer will check the minimum watermark that waiters are waiting for and if the ring buffer is past that, it will wake up all the waiters. The waiters are in a wait loop, and will first check if a signal is pending and then check if the ring buffer is at the desired level where it should break out of the loop. If a file that uses a ring buffer closes, and there's threads waiting on the ring buffer, it needs to wake up those threads. To do this, a "wait_index" was used. Before entering the wait loop, the waiter will read the wait_index. On wakeup, it will check if the wait_index is different than when it entered the loop, and will exit the loop if it is. The waker will only need to update the wait_index before waking up the waiters. This had a couple of bugs. One trivial one and one broken by design. The trivial bug was that the waiter checked the wait_index after the schedule() call. It had to be checked between the prepare_to_wait() and the schedule() which it was not. The main bug is that the first check to set the default wait_index will always be outside the prepare_to_wait() and the schedule(). That's because the ring_buffer_wait() doesn't have enough context to know if it should break out of the loop. The loop itself is not needed, because all the callers to the ring_buffer_wait() also has their own loop, as the callers have a better sense of what the context is to decide whether to break out of the loop or not. Just have the ring_buffer_wait() block once, and if it gets woken up, exit the function and let the callers decide what to do next. Link: https://lore.kernel.org/all/CAHk-=whs5MdtNjzFkTyaUy=vHi=qwWgPi0JgTe6OYUYMNSRZfg@mail.gmail.com/ Link: https://lore.kernel.org/linux-trace-kernel/20240308202431.792933613@goodmis.org Cc: stable@vger.kernel.org Cc: Masami Hiramatsu Cc: Mark Rutland Cc: Mathieu Desnoyers Cc: Andrew Morton Cc: Linus Torvalds Cc: linke li Cc: Rabin Vincent Fixes: e30f53aad2202 ("tracing: Do not busy wait in buffer splice") Signed-off-by: Steven Rostedt (Google)

tracing: Limit trace_marker writes to just 4K

2024-03-06T18:27:26Z

Limit the max print event of trace_marker to just 4K string size. This must also be less than the amount that can be held by a trace_seq along with the text that is before the output (like the task name, PID, CPU, state, etc). As trace_seq is made to handle large events (some greater than 4K). Make the max size of a trace_marker write event be 4K which is guaranteed to fit in the trace_seq buffer. Link: https://lore.kernel.org/linux-trace-kernel/20240304223433.4ba47dff@gandalf.local.home Suggested-by: Linus Torvalds Reviewed-by: Mathieu Desnoyers Reviewed-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt (Google)

tracing: Remove precision vsnprintf() check from print event

2024-03-06T18:26:26Z

This reverts 60be76eeabb3d ("tracing: Add size check when printing trace_marker output"). The only reason the precision check was added was because of a bug that miscalculated the write size of the string into the ring buffer and it truncated it removing the terminating nul byte. On reading the trace it crashed the kernel. But this was due to the bug in the code that happened during development and should never happen in practice. If anything, the precision can hide bugs where the string in the ring buffer isn't nul terminated and it will not be checked. Link: https://lore.kernel.org/all/C7E7AF1A-D30F-4D18-B8E5-AF1EF58004F5@linux.ibm.com/ Link: https://lore.kernel.org/linux-trace-kernel/20240227125706.04279ac2@gandalf.local.home Link: https://lore.kernel.org/all/20240302111244.3a1674be@gandalf.local.home/ Link: https://lore.kernel.org/linux-trace-kernel/20240304174341.2a561d9f@gandalf.local.home Cc: Masami Hiramatsu Cc: Linus Torvalds Fixes: 60be76eeabb3d ("tracing: Add size check when printing trace_marker output") Reported-by: Sachin Sant Tested-by: Sachin Sant Reviewed-by: Mathieu Desnoyers Signed-off-by: Steven Rostedt (Google)

Merge tag 'probes-fixes-v6.8-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

2024-03-01T19:17:23Z

Pull fprobe fix from Masami Hiramatsu: - allocate entry_data_size buffer for each rethook instance. This fixes a buffer overrun bug (which leads a kernel crash) when fprobe user uses its entry_data in the entry_handler. * tag 'probes-fixes-v6.8-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: fprobe: Fix to allocate entry_data_size buffer with rethook instances

fprobe: Fix to allocate entry_data_size buffer with rethook instances

2024-03-01T00:18:24Z

Fix to allocate fprobe::entry_data_size buffer with rethook instances. If fprobe doesn't allocate entry_data_size buffer for each rethook instance, fprobe entry handler can cause a buffer overrun when storing entry data in entry handler. Link: https://lore.kernel.org/all/170920576727.107552.638161246679734051.stgit@devnote2/ Reported-by: Jiri Olsa Closes: https://lore.kernel.org/all/Zd9eBn2FTQzYyg7L@krava/ Fixes: 4bbd93455659 ("kprobes: kretprobe scalability improvement") Cc: stable@vger.kernel.org Tested-by: Jiri Olsa Signed-off-by: Masami Hiramatsu (Google)

ring-buffer: Do not let subbuf be bigger than write mask

2024-02-21T14:15:23Z

The data on the subbuffer is measured by a write variable that also contains status flags. The counter is just 20 bits in length. If the subbuffer is bigger than then counter, it will fail. Make sure that the subbuffer can not be set to greater than the counter that keeps track of the data on the subbuffer. Link: https://lore.kernel.org/linux-trace-kernel/20240220095112.77e9cb81@gandalf.local.home Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Fixes: 2808e31ec12e5 ("ring-buffer: Add interface for configuring trace sub buffer size") Signed-off-by: Steven Rostedt (Google)

Merge tag 'probes-fixes-v6.8-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

2024-02-17T15:59:47Z

Pull probes fix from Masami Hiramatsu: - tracing/probes: Fix BTF structure member finder to find the members which are placed after any anonymous union member correctly. * tag 'probes-fixes-v6.8-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: tracing/probes: Fix to search structure fields correctly