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Paul E. McKenney 3cec27453d srcu: Make SRCU-fast also be NMI-safe
BPF uses rcu_read_lock_trace() in NMI context, so srcu_read_lock_fast()
must be NMI-safe if it is to have any chance of addressing RCU Tasks
Trace use cases.  This commit therefore causes srcu_read_lock_fast()
and srcu_read_unlock_fast() to use atomic_long_inc() instead of
this_cpu_inc() on architectures that support NMIs but do not have
NMI-safe implementations of this_cpu_inc().  Note that both x86 and
arm64 have NMI-safe implementations of this_cpu_inc(), and thus do not
pay the performance penalty inherent in atomic_inc_long().

It is tempting to use this trick to fold srcu_read_lock_nmisafe()
into srcu_read_lock(), but this would need careful thought, review,
and performance analysis.  Though those smp_mb() calls might well make
performance a non-issue.

Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
History 2025-02-05 07:12:06 -08:00
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Linux kernel
============

There are several guides for kernel developers and users. These guides can
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Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
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    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.