linux-kernel - Re: [PATCH] timer: Fix jiffies wrap behavior of round

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Date:	Wed, 29 May 2013 16:17:47 -0700
From:	Joe Perches <joe@...ches.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Bart Van Assche <bart.vanassche@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arjan van de Ven <arjan@...radead.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] timer: Fix jiffies wrap behavior of round_jiffies*()

On Wed, 2013-05-29 at 16:01 -0700, Andrew Morton wrote:
> On Tue, 21 May 2013 20:43:50 +0200 Bart Van Assche <bart.vanassche@...il.com> wrote:
> 
> > Make sure that the round_jiffies*() functions return a time that is
> > in the future when the jiffies counter is about to wrap.
> 
> Actually "when the jiffies counter has recently wrapped".
> 
> I assume this was found by inspection?
> 
> > @@ -149,9 +149,7 @@ static unsigned long round_jiffies_common(unsigned long j, int cpu,
> >  	/* now that we have rounded, subtract the extra skew again */
> >  	j -= cpu * 3;
> > -	if (j <= jiffies) /* rounding ate our timeout entirely; */
> 
> This used to be a very common bug - we've weeded out many instances but
> I'm sure more still remain.

This list probably isn't comprehensive.

$ git grep -E "if\s*\((\s*jiffies\s*[\<\>]|.*[\<\>]=?\s*jiffies\b)"
drivers/acpi/acpi_pad.c:                if (last_jiffies + round_robin_time * HZ < jiffies) {
drivers/acpi/acpi_pad.c:                        if (jiffies > expire_time) {
drivers/dma/ioat/dma_v2.c:      if (jiffies > chan->timer.expires && timer_pending(&chan->timer)) {
drivers/infiniband/hw/ipath/ipath_sdma.c:               if (jiffies < dd->ipath_sdma_abort_intr_timeout)
drivers/infiniband/hw/ipath/ipath_sdma.c:       if (jiffies > dd->ipath_sdma_abort_jiffies) {
drivers/infiniband/ulp/ipoib/ipoib_cm.c:                if (p && time_after_eq(jiffies, p->jiffies + IPOIB_CM_RX_UPDATE
drivers/infiniband/ulp/ipoib/ipoib_cm.c:                if (time_before_eq(jiffies, p->jiffies + IPOIB_CM_RX_TIMEOUT))
drivers/input/misc/ati_remote2.c:               if (!time_after_eq(jiffies, ar2->jiffies))
drivers/md/dm-log-userspace-base.c:     else if (jiffies < limit)
drivers/misc/sgi-gru/grumain.c:                 if (gts->ts_steal_jiffies + GRU_STEAL_DELAY < jiffies)
drivers/net/ethernet/intel/e1000/e1000_ethtool.c:               if (jiffies >= (time + 2)) {
drivers/net/ethernet/intel/e1000e/ethtool.c:            if (jiffies >= (time + 20)) {
drivers/net/ethernet/micrel/ksz884x.c:                  if (next_jiffies < jiffies)
drivers/net/ethernet/micrel/ksz884x.c:          } else if (jiffies >= hw_priv->counter[i].time) {
drivers/net/ethernet/micrel/ksz884x.c:          if (hw_priv->pme_wait <= jiffies) {
drivers/net/ethernet/neterion/vxge/vxge-main.c: if (jiffies > fifo->jiffies + HZ / 100) {
drivers/net/ethernet/neterion/vxge/vxge-main.c: if (jiffies > ring->jiffies + HZ / 100) {
drivers/net/ethernet/qlogic/qlcnic/qlcnic_hw.c:                 if (jiffies > (QLCNIC_FILTER_AGE * HZ + time)) {
drivers/net/ethernet/qlogic/qlcnic/qlcnic_hw.c:                 if (jiffies > (QLCNIC_FILTER_AGE * HZ + time)) {
drivers/net/ethernet/qlogic/qlcnic/qlcnic_io.c:                         if (jiffies > (QLCNIC_READD_AGE * HZ + time))
drivers/net/ethernet/qlogic/qlcnic/qlcnic_io.c:                 if (jiffies > (QLCNIC_READD_AGE * HZ + tmp_fil->ftime))
drivers/scsi/lpfc/lpfc_scsi.c:  if ((phba->last_ramp_down_time + QUEUE_RAMP_DOWN_INTERVAL) > jiffies) {
drivers/staging/bcm/InterfaceIdleMode.c:                if (timeout < jiffies )
drivers/staging/lustre/include/linux/libcfs/linux/linux-prim.h:                 if (jiffies > expire) {           \
drivers/staging/speakup/speakup_acntpc.c:               if (jiffies >= jiff_max && ch == SPACE) {
drivers/staging/speakup/speakup_decext.c:                       if (jiffies >= jiff_max) {
drivers/staging/speakup/speakup_decpc.c:                        if (jiffies >= jiff_max) {
drivers/staging/speakup/speakup_dectlk.c:                       if (jiffies >= jiff_max) {
kernel/timer.c: if (j <= jiffies) /* rounding ate our timeout entirely; */
net/rds/ib_send.c:                      if (ic->i_ack_queued + HZ/2 < jiffies)
net/rds/ib_send.c:                      if (send->s_queued + HZ/2 < jiffies)
net/rds/iw_send.c:                      if (ic->i_ack_queued + HZ/2 < jiffies)
net/rds/iw_send.c:                      if (send->s_queued + HZ/2 < jiffies)

>   We could perhaps have a checkpatch rule
> which looks for comparisons against jiffes (and any other
> time-measuring variables we can detect)

other variables like?

>  and tells people to use
> time_after() and friends, or time_is_*_jiffies().


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