Date: Sun, 22 Jun 2014 21:37:28 +0000 (UTC) From: Mateusz Guzik <mjg@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r267755 - head/sys/kern Message-ID: <201406222137.s5MLbSHx084527@svn.freebsd.org>
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Author: mjg Date: Sun Jun 22 21:37:27 2014 New Revision: 267755 URL: http://svnweb.freebsd.org/changeset/base/267755 Log: Don't take filedesc lock in fdunshare(). We can read refcnt safely and only care if it is equal to 1. If it could suddenly change from 1 to something bigger the code would be buggy even in the previous form and transitions from > 1 to 1 are equally racy and harmless (we copy even though there is no need). MFC after: 1 week Modified: head/sys/kern/kern_descrip.c Modified: head/sys/kern/kern_descrip.c ============================================================================== --- head/sys/kern/kern_descrip.c Sun Jun 22 21:28:05 2014 (r267754) +++ head/sys/kern/kern_descrip.c Sun Jun 22 21:37:27 2014 (r267755) @@ -1852,17 +1852,14 @@ fdshare(struct filedesc *fdp) void fdunshare(struct proc *p, struct thread *td) { + struct filedesc *tmp; - FILEDESC_XLOCK(p->p_fd); - if (p->p_fd->fd_refcnt > 1) { - struct filedesc *tmp; - - FILEDESC_XUNLOCK(p->p_fd); - tmp = fdcopy(p->p_fd); - fdescfree(td); - p->p_fd = tmp; - } else - FILEDESC_XUNLOCK(p->p_fd); + if (p->p_fd->fd_refcnt == 1) + return; + + tmp = fdcopy(p->p_fd); + fdescfree(td); + p->p_fd = tmp; } /*
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