Module Name: src Committed By: riastradh Date: Fri Feb 24 11:21:29 UTC 2023
Modified Files: src/sys/kern: kern_mutex.c Log Message: mutex(9): Simplify membars. - Elide macro indirection for membar_acquire. - Use atomic_store_release instead of membar_release and store. No functional change intended. Possible very very very very minor performance gain on architectures with a native store-release instruction. Note: It is possible there are some code paths that worked by accident with this change which could, in theory, break now, such as the logic I recently fixed in kern_descrip.c that assumed a mutex_enter/exit cycle would serve as a store-before-store barrier: fp->f_... = ...; // A /* fd_affix */ mutex_enter(&fp->f_lock); fp->f_count++; mutex_exit(&fp->f_lock); ... ff->ff_file = fp; // B This logic was never correct, and is likely already broken in practice on aarch64 because the mutex_exit stub already uses STLXR instead of DMB ISH(ST); STXR. This change only affects the slow path of mutex_exit, so it doesn't change even the accidental guarantees mutex_exit makes in all paths. To generate a diff of this commit: cvs rdiff -u -r1.103 -r1.104 src/sys/kern/kern_mutex.c Please note that diffs are not public domain; they are subject to the copyright notices on the relevant files.