> Il giorno 04 apr 2017, alle ore 17:28, Bart Van Assche <bart.vanassche@xxxxxxxxxxx> ha scritto: > > On Tue, 2017-04-04 at 12:42 +0200, Paolo Valente wrote: >>> Il giorno 31 mar 2017, alle ore 17:31, Bart Van Assche <bart.vanassche@xxxxxxxxxxx> ha scritto: >>> >>> On Fri, 2017-03-31 at 14:47 +0200, Paolo Valente wrote: >>>> + delta_ktime = ktime_get(); >>>> + delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start); >>>> + delta_usecs = ktime_to_us(delta_ktime); >>> >>> This patch changes the type of the variable in which the result of ktime_to_us() >>> is stored from u64 into u32 and next compares that result with LONG_MAX. Since >>> ktime_to_us() returns a signed 64-bit number, are you sure you want to store that >>> result in a 32-bit variable? If ktime_to_us() would e.g. return 0xffffffff00000100 >>> or 0x100000100 then the assignment will truncate these numbers to 0x100. >> >> The instruction above the assignment you highlight stores in >> delta_ktime the difference between 'now' and the last budget start. >> The latter may have happened at most about 100 ms before 'now'. So >> there should be no overflow issue. > > Hello Paolo, > > Please double check the following code: if (delta_usecs < 1000 || delta_usecs >= LONG_MAX) > Since delta_usecs is a 32-bit variable and LONG_MAX a 64-bit constant on 64-bit systems > I'm not sure that code will do what it is intended to do. > Yes, sorry. Actually, it never occurred to me to see that extra condition to hold over the last eight years on 32-bit systems. So I think I will just remove it. Unless Fabio, who inserted that condition several years ago, has something to say. Thanks, Paolo > Thanks, > > Bart.
