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Add sleepable implementations of bpf_get_stack() and bpf_get_task_stack() helpers and allow them to be used from sleepable BPF program (e.g., sleepable uprobes). Note, the stack trace IPs capturing itself is not sleepable (that would need to be a separate project), only build ID fetching is sleepable and thus more reliable, as it will wait for data to be paged in, if necessary. For that we make use of sleepable build_id_parse() implementation. Now that build ID related internals in kernel/bpf/stackmap.c can be used both in sleepable and non-sleepable contexts, we need to add additional rcu_read_lock()/rcu_read_unlock() protection around fetching perf_callchain_entry, but with the refactoring in previous commit it's now pretty straightforward. We make sure to do rcu_read_unlock (in sleepable mode only) right before stack_map_get_build_id_offset() call which can sleep. By that time we don't have any more use of perf_callchain_entry. Note, bpf_get_task_stack() will fail for user mode if task != current. And for kernel mode build ID are irrelevant. So in that sense adding sleepable bpf_get_task_stack() implementation is a no-op. It feel right to wire this up for symmetry and completeness, but I'm open to just dropping it until we support `user && crosstask` condition. Reviewed-by: Eduard Zingerman <eddyz87@gmail.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/r/20240829174232.3133883-10-andrii@kernel.org 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.