Date: Mon, 05 Jan 2015 18:48:26 +0100 From: Hans Petter Selasky <hps@selasky.org> To: John Baldwin <jhb@FreeBSD.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r276534 - head/sys/dev/vt Message-ID: <54AACE6A.7020702@selasky.org> In-Reply-To: <54AACBC4.5040802@FreeBSD.org> References: <201501021335.t02DZBRm015072@svn.freebsd.org> <54AACBC4.5040802@FreeBSD.org>
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On 01/05/15 18:37, John Baldwin wrote: > On 1/2/15 8:35 AM, Hans Petter Selasky wrote: >> Author: hselasky >> Date: Fri Jan 2 13:35:10 2015 >> New Revision: 276534 >> URL: https://svnweb.freebsd.org/changeset/base/276534 >> >> Log: >> The "vt_suspend_flush_timer()" function is sometimes called locked >> which prevents us from doing a "callout_drain()" call. The callout in >> question has a lock associated with it and we are not freeing the >> callout. That means we can use the "callout_stop()" function to >> atomically stop the callback iff the "callout_stop()" function is >> called locked. This patch applies proper locking to "callout_stop()" >> and replaces a "callout_drain()" with a "callout_stop()". >> >> Modified: head/sys/dev/vt/vt_core.c >> ============================================================================== >> --- head/sys/dev/vt/vt_core.c Fri Jan 2 13:15:36 2015 (r276533) >> +++ head/sys/dev/vt/vt_core.c Fri Jan 2 13:35:10 2015 (r276534) >> @@ -114,6 +114,7 @@ const struct terminal_class vt_termclass >> >> #define VT_LOCK(vd) mtx_lock(&(vd)->vd_lock) >> #define VT_UNLOCK(vd) mtx_unlock(&(vd)->vd_lock) >> +#define VT_LOCK_ASSERT(vd, what) mtx_assert(&(vd)->vd_lock, what) >> >> #define VT_UNIT(vw) ((vw)->vw_device->vd_unit * VT_MAXWINDOWS + \ >> (vw)->vw_number) >> @@ -283,12 +284,18 @@ vt_resume_flush_timer(struct vt_device * >> static void >> vt_suspend_flush_timer(struct vt_device *vd) >> { >> + /* >> + * As long as this function is called locked, callout_stop() >> + * has the same effect like callout_drain() with regard to >> + * preventing the callback function from executing. >> + */ >> + VT_LOCK_ASSERT(vd, MA_OWNED); > > Note that this assert is redundant. callout_stop() already asserts this > for a callout initialized via callout_init_mtx(). > Right, but there is an "if" there which not always makes the assert visible execept for static code analysis. --HPS
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