Date: Thu, 25 May 2017 17:23:26 +0000 (UTC) From: Don Lewis <truckman@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-10@freebsd.org Subject: svn commit: r318886 - stable/10/sys/netpfil/ipfw Message-ID: <201705251723.v4PHNQb0028042@repo.freebsd.org>
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Author: truckman Date: Thu May 25 17:23:26 2017 New Revision: 318886 URL: https://svnweb.freebsd.org/changeset/base/318886 Log: MFC r318511 The result of right shifting a negative signed value is implementation defined. On machines without arithmetic shift instructions, zero bits may be shifted in from the left, giving a large positive result instead of the desired divide-by power-of-2. Fix this by operating on the absolute value and compensating for the possible negation later. Reverse the order of the underflow/overflow tests and the exponential decay calculation to avoid the possibility of an erroneous overflow detection if p is a sufficiently small non-negative value. Also check for negative values of prob before doing the exponential decay to avoid another instance of of right shifting a negative value. Tested by: Rasool Al-Saadi <ralsaadi@swin.edu.au> Modified: stable/10/sys/netpfil/ipfw/dn_aqm_pie.c stable/10/sys/netpfil/ipfw/dn_sched_fq_pie.c Directory Properties: stable/10/ (props changed) Modified: stable/10/sys/netpfil/ipfw/dn_aqm_pie.c ============================================================================== --- stable/10/sys/netpfil/ipfw/dn_aqm_pie.c Thu May 25 17:22:13 2017 (r318885) +++ stable/10/sys/netpfil/ipfw/dn_aqm_pie.c Thu May 25 17:23:26 2017 (r318886) @@ -206,6 +206,7 @@ calculate_drop_prob(void *x) int64_t p, prob, oldprob; struct dn_aqm_pie_parms *pprms; struct pie_status *pst = (struct pie_status *) x; + int p_isneg; pprms = pst->parms; prob = pst->drop_prob; @@ -221,6 +222,12 @@ calculate_drop_prob(void *x) ((int64_t)pst->current_qdelay - (int64_t)pprms->qdelay_ref); p +=(int64_t) pprms->beta * ((int64_t)pst->current_qdelay - (int64_t)pst->qdelay_old); + + /* take absolute value so right shift result is well defined */ + p_isneg = p < 0; + if (p_isneg) { + p = -p; + } /* We PIE_MAX_PROB shift by 12-bits to increase the division precision */ p *= (PIE_MAX_PROB << 12) / AQM_TIME_1S; @@ -243,37 +250,47 @@ calculate_drop_prob(void *x) oldprob = prob; - /* Cap Drop adjustment */ - if ((pprms->flags & PIE_CAPDROP_ENABLED) && prob >= PIE_MAX_PROB / 10 - && p > PIE_MAX_PROB / 50 ) - p = PIE_MAX_PROB / 50; + if (p_isneg) { + prob = prob - p; - prob = prob + p; - - /* decay the drop probability exponentially */ - if (pst->current_qdelay == 0 && pst->qdelay_old == 0) - /* 0.98 ~= 1- 1/64 */ - prob = prob - (prob >> 6); + /* check for multiplication underflow */ + if (prob > oldprob) { + prob= 0; + D("underflow"); + } + } else { + /* Cap Drop adjustment */ + if ((pprms->flags & PIE_CAPDROP_ENABLED) && + prob >= PIE_MAX_PROB / 10 && + p > PIE_MAX_PROB / 50 ) { + p = PIE_MAX_PROB / 50; + } + prob = prob + p; - /* check for multiplication overflow/underflow */ - if (p>0) { + /* check for multiplication overflow */ if (prob<oldprob) { D("overflow"); prob= PIE_MAX_PROB; } } - else - if (prob>oldprob) { - prob= 0; - D("underflow"); - } - /* make drop probability between 0 and PIE_MAX_PROB*/ - if (prob < 0) + /* + * decay the drop probability exponentially + * and restrict it to range 0 to PIE_MAX_PROB + */ + if (prob < 0) { prob = 0; - else if (prob > PIE_MAX_PROB) - prob = PIE_MAX_PROB; + } else { + if (pst->current_qdelay == 0 && pst->qdelay_old == 0) { + /* 0.98 ~= 1- 1/64 */ + prob = prob - (prob >> 6); + } + + if (prob > PIE_MAX_PROB) { + prob = PIE_MAX_PROB; + } + } pst->drop_prob = prob; Modified: stable/10/sys/netpfil/ipfw/dn_sched_fq_pie.c ============================================================================== --- stable/10/sys/netpfil/ipfw/dn_sched_fq_pie.c Thu May 25 17:22:13 2017 (r318885) +++ stable/10/sys/netpfil/ipfw/dn_sched_fq_pie.c Thu May 25 17:23:26 2017 (r318886) @@ -377,6 +377,7 @@ fq_calculate_drop_prob(void *x) struct dn_aqm_pie_parms *pprms; int64_t p, prob, oldprob; aqm_time_t now; + int p_isneg; now = AQM_UNOW; pprms = pst->parms; @@ -393,6 +394,12 @@ fq_calculate_drop_prob(void *x) ((int64_t)pst->current_qdelay - (int64_t)pprms->qdelay_ref); p +=(int64_t) pprms->beta * ((int64_t)pst->current_qdelay - (int64_t)pst->qdelay_old); + + /* take absolute value so right shift result is well defined */ + p_isneg = p < 0; + if (p_isneg) { + p = -p; + } /* We PIE_MAX_PROB shift by 12-bits to increase the division precision */ p *= (PIE_MAX_PROB << 12) / AQM_TIME_1S; @@ -415,37 +422,47 @@ fq_calculate_drop_prob(void *x) oldprob = prob; - /* Cap Drop adjustment */ - if ((pprms->flags & PIE_CAPDROP_ENABLED) && prob >= PIE_MAX_PROB / 10 - && p > PIE_MAX_PROB / 50 ) - p = PIE_MAX_PROB / 50; + if (p_isneg) { + prob = prob - p; - prob = prob + p; - - /* decay the drop probability exponentially */ - if (pst->current_qdelay == 0 && pst->qdelay_old == 0) - /* 0.98 ~= 1- 1/64 */ - prob = prob - (prob >> 6); + /* check for multiplication underflow */ + if (prob > oldprob) { + prob= 0; + D("underflow"); + } + } else { + /* Cap Drop adjustment */ + if ((pprms->flags & PIE_CAPDROP_ENABLED) && + prob >= PIE_MAX_PROB / 10 && + p > PIE_MAX_PROB / 50 ) { + p = PIE_MAX_PROB / 50; + } + prob = prob + p; - /* check for multiplication over/under flow */ - if (p>0) { + /* check for multiplication overflow */ if (prob<oldprob) { D("overflow"); prob= PIE_MAX_PROB; } } - else - if (prob>oldprob) { - prob= 0; - D("underflow"); - } - /* make drop probability between 0 and PIE_MAX_PROB*/ - if (prob < 0) + /* + * decay the drop probability exponentially + * and restrict it to range 0 to PIE_MAX_PROB + */ + if (prob < 0) { prob = 0; - else if (prob > PIE_MAX_PROB) - prob = PIE_MAX_PROB; + } else { + if (pst->current_qdelay == 0 && pst->qdelay_old == 0) { + /* 0.98 ~= 1- 1/64 */ + prob = prob - (prob >> 6); + } + + if (prob > PIE_MAX_PROB) { + prob = PIE_MAX_PROB; + } + } pst->drop_prob = prob;
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