Date: Sun, 10 Feb 2019 23:07:47 +0000 (UTC) From: Conrad Meyer <cem@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r343985 - head/sys/kern Message-ID: <201902102307.x1AN7lj8011617@repo.freebsd.org>
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Author: cem Date: Sun Feb 10 23:07:46 2019 New Revision: 343985 URL: https://svnweb.freebsd.org/changeset/base/343985 Log: Prevent overflow for usertime/systime in caclru1 PR: 76972 and duplicates Reported by: Dr. Christopher Landauer <cal AT aero.org>, Steinar Haug <sthaug AT nethelp.no> Submitted by: Andrey Zonov <andrey AT zonov.org> (earlier version) MFC after: 2 weeks Modified: head/sys/kern/kern_resource.c Modified: head/sys/kern/kern_resource.c ============================================================================== --- head/sys/kern/kern_resource.c Sun Feb 10 22:33:41 2019 (r343984) +++ head/sys/kern/kern_resource.c Sun Feb 10 23:07:46 2019 (r343985) @@ -863,6 +863,15 @@ rufetchtd(struct thread *td, struct rusage *ru) calcru1(p, &td->td_rux, &ru->ru_utime, &ru->ru_stime); } +static uint64_t +mul64_by_fraction(uint64_t a, uint64_t b, uint64_t c) +{ + /* + * Compute floor(a * (b / c)) without overflowing, (b / c) <= 1.0. + */ + return ((a / c) * b + (a % c) * (b / c) + (a % c) * (b % c) / c); +} + static void calcru1(struct proc *p, struct rusage_ext *ruxp, struct timeval *up, struct timeval *sp) @@ -892,10 +901,10 @@ calcru1(struct proc *p, struct rusage_ext *ruxp, struc * The normal case, time increased. * Enforce monotonicity of bucketed numbers. */ - uu = (tu * ut) / tt; + uu = mul64_by_fraction(tu, ut, tt); if (uu < ruxp->rux_uu) uu = ruxp->rux_uu; - su = (tu * st) / tt; + su = mul64_by_fraction(tu, st, tt); if (su < ruxp->rux_su) su = ruxp->rux_su; } else if (tu + 3 > ruxp->rux_tu || 101 * tu > 100 * ruxp->rux_tu) { @@ -924,8 +933,8 @@ calcru1(struct proc *p, struct rusage_ext *ruxp, struc "to %ju usec for pid %d (%s)\n", (uintmax_t)ruxp->rux_tu, (uintmax_t)tu, p->p_pid, p->p_comm); - uu = (tu * ut) / tt; - su = (tu * st) / tt; + uu = mul64_by_fraction(tu, ut, tt); + su = mul64_by_fraction(tu, st, tt); } ruxp->rux_uu = uu;
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