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c69993ecdd
Add support for deferred userspace unwind to perf. Where perf currently relies on in-place stack unwinding; from NMI context and all that. This moves the userspace part of the unwind to right before the return-to-userspace. This has two distinct benefits, the biggest is that it moves the unwind to a faultable context. It becomes possible to fault in debug info (.eh_frame, SFrame etc.) that might not otherwise be readily available. And secondly, it de-duplicates the user callchain where multiple samples happen during the same kernel entry. To facilitate this the perf interface is extended with a new record type: PERF_RECORD_CALLCHAIN_DEFERRED and two new attribute flags: perf_event_attr::defer_callchain - to request the user unwind be deferred perf_event_attr::defer_output - to request PERF_RECORD_CALLCHAIN_DEFERRED records The existing PERF_RECORD_SAMPLE callchain section gets a new context type: PERF_CONTEXT_USER_DEFERRED After which will come a single entry, denoting the 'cookie' of the deferred callchain that should be attached here, matching the 'cookie' field of the above mentioned PERF_RECORD_CALLCHAIN_DEFERRED. The 'defer_callchain' flag is expected on all events with PERF_SAMPLE_CALLCHAIN. The 'defer_output' flag is expect on the event responsible for collecting side-band events (like mmap, comm etc.). Setting 'defer_output' on multiple events will get you duplicated PERF_RECORD_CALLCHAIN_DEFERRED records. Based on earlier patches by Josh and Steven. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://patch.msgid.link/20251023150002.GR4067720@noisy.programming.kicks-ass.net
80 lines
2.1 KiB
C
80 lines
2.1 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_UNWIND_USER_DEFERRED_H
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#define _LINUX_UNWIND_USER_DEFERRED_H
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#include <linux/task_work.h>
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#include <linux/unwind_user.h>
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#include <linux/unwind_deferred_types.h>
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#ifdef CONFIG_UNWIND_USER
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enum {
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UNWIND_PENDING_BIT = 0,
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UNWIND_USED_BIT,
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};
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enum {
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UNWIND_PENDING = BIT(UNWIND_PENDING_BIT),
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/* Set if the unwinding was used (directly or deferred) */
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UNWIND_USED = BIT(UNWIND_USED_BIT)
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};
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void unwind_task_init(struct task_struct *task);
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void unwind_task_free(struct task_struct *task);
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int unwind_user_faultable(struct unwind_stacktrace *trace);
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int unwind_deferred_init(struct unwind_work *work, unwind_callback_t func);
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int unwind_deferred_request(struct unwind_work *work, u64 *cookie);
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void unwind_deferred_cancel(struct unwind_work *work);
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void unwind_deferred_task_exit(struct task_struct *task);
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static __always_inline void unwind_reset_info(void)
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{
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struct unwind_task_info *info = ¤t->unwind_info;
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unsigned long bits = atomic_long_read(&info->unwind_mask);
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/* Was there any unwinding? */
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if (likely(!bits))
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return;
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do {
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/* Is a task_work going to run again before going back */
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if (bits & UNWIND_PENDING)
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return;
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} while (!atomic_long_try_cmpxchg(&info->unwind_mask, &bits, 0UL));
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current->unwind_info.id.id = 0;
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if (unlikely(info->cache)) {
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info->cache->nr_entries = 0;
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info->cache->unwind_completed = 0;
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}
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}
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#else /* !CONFIG_UNWIND_USER */
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static inline void unwind_task_init(struct task_struct *task) {}
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static inline void unwind_task_free(struct task_struct *task) {}
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static inline int unwind_user_faultable(struct unwind_stacktrace *trace)
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{ return -ENOSYS; }
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static inline int
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unwind_deferred_init(struct unwind_work *work, unwind_callback_t func)
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{ return -ENOSYS; }
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static inline int
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unwind_deferred_request(struct unwind_work *work, u64 *timestamp)
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{ return -ENOSYS; }
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static inline void unwind_deferred_cancel(struct unwind_work *work) {}
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static inline void unwind_deferred_task_exit(struct task_struct *task) {}
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static inline void unwind_reset_info(void) {}
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#endif /* !CONFIG_UNWIND_USER */
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#endif /* _LINUX_UNWIND_USER_DEFERRED_H */
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