On Tue, Aug 26, 2014 at 5:55 PM, Jens Axboe <ax...@fb.com> wrote: > On 08/26/2014 08:47 AM, Alexey Dobriyan wrote: >> Found and reproduced some time ago, almost forgot about :-) >> >> In part_round_stats_single(), ->stamp field is written but without >> locking SMP-wise. >> >> part->stamp = now; >> >> So, if two processes read /proc/diskstats, it is possible for "now - >> part->stamp" value to become negative. >> >> And indeed this can happen: >> >> now 4294755500, ->stamp 4294755501 >> ------------[ cut here ]------------ >> WARNING: CPU: 0 PID: 1950 at block/blk-core.c:1229 >> part_round_stats_single+0xc0/0xd0() >> ... >> [<ffffffff811963f0>] part_round_stats_single+0xc0/0xd0 >> [<ffffffff81196447>] part_round_stats+0x47/0x70 >> [<ffffffff811a069d>] diskstats_show+0x8d/0x4b0 >> ... >> >> Dunno how important used fields in /proc/diskstats but they can be >> clearly bogus. > > Easiest fix is probably just to do the now - part->stamp math earlier, > and ignore <= 0 instead of just now == part->stamp. I think that should > be good enough for disk stats, and (most importantly), it would avoid > the warning. > > Speaking of the warning, I don't see where that is. Where is it from?
I inserted the warning to be sure bug exists and I am not misreading the code. Alexey -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
