Date: Mon, 10 Feb 2020 16:52:51 -0800 From: Gleb Smirnoff <glebius@freebsd.org> To: Mateusz Guzik <mjg@freebsd.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r357728 - head/sys/sys Message-ID: <20200211005251.GA1351@FreeBSD.org> In-Reply-To: <202002101352.01ADqQLh039003@repo.freebsd.org> References: <202002101352.01ADqQLh039003@repo.freebsd.org>
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On Mon, Feb 10, 2020 at 01:52:26PM +0000, Mateusz Guzik wrote: M> Author: mjg M> Date: Mon Feb 10 13:52:25 2020 M> New Revision: 357728 M> URL: https://svnweb.freebsd.org/changeset/base/357728 M> M> Log: M> Tidy up zpcpu_replace* M> M> - only compute the target address once M> - remove spurious type casting, zpcpu_get already return the correct type M> M> While here add missing newlines to other routines. M> M> Modified: M> head/sys/sys/pcpu.h M> M> Modified: head/sys/sys/pcpu.h M> ============================================================================== M> --- head/sys/sys/pcpu.h Mon Feb 10 13:24:14 2020 (r357727) M> +++ head/sys/sys/pcpu.h Mon Feb 10 13:52:25 2020 (r357728) M> @@ -245,32 +245,41 @@ extern struct pcpu *cpuid_to_pcpu[]; M> * If you need atomicity use xchg. M> * */ M> #define zpcpu_replace(base, val) ({ \ M> - __typeof(val) _old = *(__typeof(base))zpcpu_get(base); \ M> - *(__typeof(val) *)zpcpu_get(base) = val; \ M> + __typeof(val) *_ptr = zpcpu_get(base); \ M> + __typeof(val) _old; \ M> + \ M> + _old = *_ptr; \ M> + *_ptr = val; \ M> _old; \ M> }) I think this function must have only protected variant that asserts that curthread->td_critnest is on. zpcpu_get() sometimes can be used without critical section, when we are fine with getting a value from a different CPU. However, can't imagine a situation where migrating during a replace operation is acceptable. -- Gleb Smirnoff
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