Date: Fri, 5 Dec 2014 15:02:31 +0000 (UTC) From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r275513 - head/sys/vm Message-ID: <201412051502.sB5F2V7g066261@svn.freebsd.org>
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Author: kib Date: Fri Dec 5 15:02:30 2014 New Revision: 275513 URL: https://svnweb.freebsd.org/changeset/base/275513 Log: When the last reference on the vnode' vm object is dropped, read the vp->v_vflag without taking vnode lock and without bypass. We do know that vp is the lowest level in the stack, since the pointer is obtained from the object' handle. Stale VV_TEXT flag read can only happen if parallel execve() is performed and not yet activated the image, since process takes reference for text mapping. In this case, the execve() code manages the VV_TEXT flag on its own already. It was observed that otherwise read-only sendfile(2) requires exclusive vnode lock and contending on it on some loads for VV_TEXT handling. Reported by: glebius, scottl Tested by: glebius, pho Sponsored by: The FreeBSD Foundation MFC after: 1 week Modified: head/sys/vm/vm_object.c Modified: head/sys/vm/vm_object.c ============================================================================== --- head/sys/vm/vm_object.c Fri Dec 5 13:30:45 2014 (r275512) +++ head/sys/vm/vm_object.c Fri Dec 5 15:02:30 2014 (r275513) @@ -468,7 +468,12 @@ vm_object_vndeallocate(vm_object_t objec } #endif - if (object->ref_count > 1) { + /* + * The test for text of vp vnode does not need a bypass to + * reach right VV_TEXT there, since it is obtained from + * object->handle. + */ + if (object->ref_count > 1 || (vp->v_vflag & VV_TEXT) == 0) { object->ref_count--; VM_OBJECT_WUNLOCK(object); /* vrele may need the vnode lock. */
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