| Message ID | 1478594694-98847-1-git-send-email-jthumshirn@suse.de (mailing list archive) |
|---|---|
| State | Changes Requested, archived |
| Headers | show |
On 11/08/16 00:45, Johannes Thumshirn wrote: > Commit 540eb1eef 'scsi: libfc: fix seconds_since_last_reset calculation' > removed the use of 'struct timespec' from fc_get_host_stats(). This broke the > output of 'fcoeadm -s' after kernel 4.8-rc1 as lport->boot_time - jiffies > could become negative as in this example: > > $ cat /sys/class/fc_host/host8/statistics/seconds_since_last_reset > 0x10624dd2f1977b4 > > Take this into account so > /sys/class/fc_host/hostX/statistics/seconds_since_last_reset is sane again. > > Fixes: 540eb1eef ('scsi: libfc: fix seconds_since_last_reset calculation') > Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de> > Tested-by: Holger Schranz <holger@fam-schranz.de> > --- > drivers/scsi/libfc/fc_lport.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/drivers/scsi/libfc/fc_lport.c b/drivers/scsi/libfc/fc_lport.c > index 04ce7cf..475c0a9 100644 > --- a/drivers/scsi/libfc/fc_lport.c > +++ b/drivers/scsi/libfc/fc_lport.c > @@ -304,11 +304,15 @@ struct fc_host_statistics *fc_get_host_stats(struct Scsi_Host *shost) > unsigned int cpu; > u64 fcp_in_bytes = 0; > u64 fcp_out_bytes = 0; > + unsigned long boot_time = lport->boot_time; > > fc_stats = &lport->host_stats; > memset(fc_stats, 0, sizeof(struct fc_host_statistics)); > > - fc_stats->seconds_since_last_reset = (lport->boot_time - jiffies) / HZ; > + if (boot_time > jiffies) > + fc_stats->seconds_since_last_reset = (boot_time - jiffies) / HZ; > + else > + fc_stats->seconds_since_last_reset = (jiffies - boot_time) / HZ; > > for_each_possible_cpu(cpu) { > struct fc_stats *stats; Hello Johannes, I think the above code will miscalculate seconds_since_last_reset if 'jiffies' wraps around after an lport has been created and before seconds_since_last_reset is computed. Shouldn't seconds_since_last_reset be computed as follows? fc_stats->seconds_since_last_reset = (jiffies - boot_time) / HZ; Bart. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, Nov 08, 2016 at 03:04:43PM +0000, Bart Van Assche wrote: [...] > Hello Johannes, > > I think the above code will miscalculate seconds_since_last_reset if > 'jiffies' wraps around after an lport has been created and before > seconds_since_last_reset is computed. Shouldn't seconds_since_last_reset > be computed as follows? > > fc_stats->seconds_since_last_reset = (jiffies - boot_time) / HZ; But what happens when jiffies - boot_time becomes negative? Then we reintroduce the bug again and have 'fcoeadm -s' show weird values. Byte, Johannes
On Tue, 2016-11-15 at 10:18 +0100, Johannes Thumshirn wrote: > On Tue, Nov 08, 2016 at 03:04:43PM +0000, Bart Van Assche wrote: > > I think the above code will miscalculate seconds_since_last_reset > > if > > 'jiffies' wraps around after an lport has been created and before > > seconds_since_last_reset is computed. Shouldn't > > seconds_since_last_reset > > be computed as follows? > > > > fc_stats->seconds_since_last_reset = (jiffies - boot_time) / > > HZ; > > But what happens when jiffies - boot_time becomes negative? Then we > reintroduce the bug again and have 'fcoeadm -s' show weird values. Hello Johannes, If your concern is about 'jiffies' wrapping around on 32-bit systems then you should use get_jiffies_64(). get_jiffies_64() - boot_time can't become negative. It namely takes several million years before a 64-bit HZ counter wraps around. Bart.
On Tue, Nov 15, 2016 at 02:50:17PM +0000, Bart Van Assche wrote: > On Tue, 2016-11-15 at 10:18 +0100, Johannes Thumshirn wrote: > > On Tue, Nov 08, 2016 at 03:04:43PM +0000, Bart Van Assche wrote: > > > I think the above code will miscalculate seconds_since_last_reset > > > if > > > 'jiffies' wraps around after an lport has been created and before > > > seconds_since_last_reset is computed. Shouldn't > > > seconds_since_last_reset > > > be computed as follows? > > > > > > fc_stats->seconds_since_last_reset = (jiffies - boot_time) / > > > HZ; > > > > But what happens when jiffies - boot_time becomes negative? Then we > > reintroduce the bug again and have 'fcoeadm -s' show weird values. > > Hello Johannes, > > If your concern is about 'jiffies' wrapping around on 32-bit systems > then you should use get_jiffies_64(). get_jiffies_64() - boot_time > can't become negative. It namely takes several million years before a > 64-bit HZ counter wraps around. You're right. I'll respin using get_jiffies_64() and resent once it is tested. Byte, Johannes
diff --git a/drivers/scsi/libfc/fc_lport.c b/drivers/scsi/libfc/fc_lport.c index 04ce7cf..475c0a9 100644 --- a/drivers/scsi/libfc/fc_lport.c +++ b/drivers/scsi/libfc/fc_lport.c @@ -304,11 +304,15 @@ struct fc_host_statistics *fc_get_host_stats(struct Scsi_Host *shost) unsigned int cpu; u64 fcp_in_bytes = 0; u64 fcp_out_bytes = 0; + unsigned long boot_time = lport->boot_time; fc_stats = &lport->host_stats; memset(fc_stats, 0, sizeof(struct fc_host_statistics)); - fc_stats->seconds_since_last_reset = (lport->boot_time - jiffies) / HZ; + if (boot_time > jiffies) + fc_stats->seconds_since_last_reset = (boot_time - jiffies) / HZ; + else + fc_stats->seconds_since_last_reset = (jiffies - boot_time) / HZ; for_each_possible_cpu(cpu) { struct fc_stats *stats;
Commit 540eb1eef 'scsi: libfc: fix seconds_since_last_reset calculation' removed the use of 'struct timespec' from fc_get_host_stats(). This broke the output of 'fcoeadm -s' after kernel 4.8-rc1 as lport->boot_time - jiffies could become negative as in this example: $ cat /sys/class/fc_host/host8/statistics/seconds_since_last_reset 0x10624dd2f1977b4 Take this into account so /sys/class/fc_host/hostX/statistics/seconds_since_last_reset is sane again. Fixes: 540eb1eef ('scsi: libfc: fix seconds_since_last_reset calculation') Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de> Tested-by: Holger Schranz <holger@fam-schranz.de> --- drivers/scsi/libfc/fc_lport.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)