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Mykyta Yatsenko says: ==================== bpf: Introduce deferred task context execution From: Mykyta Yatsenko <yatsenko@meta.com> This patch introduces a new mechanism for BPF programs to schedule deferred execution in the context of a specific task using the kernel’s task_work infrastructure. The new bpf_task_work interface enables BPF use cases that require sleepable subprogram execution within task context, for example, scheduling sleepable function from the context that does not allow sleepable, such as NMI. Introduced kfuncs bpf_task_work_schedule_signal() and bpf_task_work_schedule_resume() for scheduling BPF callbacks correspond to different modes used by task_work (TWA_SIGNAL or TWA_RESUME). The implementation manages scheduling state via metadata objects (struct bpf_task_work_context). Pointers to bpf_task_work_context are stored in BPF map values. State transitions are handled via an atomic state machine (bpf_task_work_state) to ensure correctness under concurrent usage and deletion, lifetime is guarded by refcounting and RCU Tasks Trace. Kfuncs call task_work_add() indirectly via irq_work to avoid locking in potentially NMI context. Changelog: --- v7 -> v8 v7: https://lore.kernel.org/bpf/20250922232611.614512-1-mykyta.yatsenko5@gmail.com/ * Fix unused variable warning in patch 1 * Decrease stress test time from 2 to 1 second * Went through CI warnings, other than unused variable, there are just 2 new in kernel/bpf/helpers.c related to newly introduced kfuncs, these look expected. v6 -> v7 v6: https://lore.kernel.org/bpf/20250918132615.193388-1-mykyta.yatsenko5@gmail.com/ * Added stress test * Extending refactoring in patch 1 * Changing comment and removing one check for map->usercnt in patch 7 v5 -> v6 v5: https://lore.kernel.org/bpf/20250916233651.258458-1-mykyta.yatsenko5@gmail.com/ * Fixing readability in verifier.c:check_map_field_pointer() * Removing BUG_ON from helpers.c v4 -> v5 v4: https://lore.kernel.org/all/20250915201820.248977-1-mykyta.yatsenko5@gmail.com/ * Fix invalid/null pointer dereference bug, reported by syzbot * Nits in selftests v3 -> v4 v3: https://lore.kernel.org/all/20250905164508.1489482-1-mykyta.yatsenko5@gmail.com/ * Modify async callback return value processing in verifier, to allow non-zero return values. * Change return type of the callback from void to int, as verifier expects scalar value. * Switched to void* for bpf_map API kfunc arguments to avoid casts. * Addressing numerous nits and small improvements. v2 -> v3 v2: https://lore.kernel.org/all/20250815192156.272445-1-mykyta.yatsenko5@gmail.com/ * Introduce ref counting * Add patches with minor verifier and btf.c refactorings to avoid code duplication * Rework initiation of the task work scheduling to handle race with map usercnt dropping to zero ==================== Link: https://patch.msgid.link/20250923112404.668720-1-mykyta.yatsenko5@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.