Re: /sys/kernel/debug/kmemleak empty despite kmemleak reports

[Catalin Marinas <catalin.marinas@arm.com>]

On Thu, Jul 09, 2020 at 11:08:52PM +0200, Paul Menzel wrote:
> Am 09.07.20 um 19:57 schrieb Catalin Marinas:
> > On Thu, Jul 09, 2020 at 04:37:10PM +0200, Paul Menzel wrote:
> > > Despite Linux 5.8-rc4 reporting memory leaks on the IBM POWER 8 S822LC, the
> > > file does not contain more information.
> > > 
> > > > $ dmesg
> > > > […] > [48662.953323] perf: interrupt took too long (2570 > 2500), lowering kernel.perf_event_max_sample_rate to 77750
> > > > [48854.810636] perf: interrupt took too long (3216 > 3212), lowering kernel.perf_event_max_sample_rate to 62000
> > > > [52300.044518] perf: interrupt took too long (4244 > 4020), lowering kernel.perf_event_max_sample_rate to 47000
> > > > [52751.373083] perf: interrupt took too long (5373 > 5305), lowering kernel.perf_event_max_sample_rate to 37000
> > > > [53354.000363] perf: interrupt took too long (6793 > 6716), lowering kernel.perf_event_max_sample_rate to 29250
> > > > [53850.215606] perf: interrupt took too long (8672 > 8491), lowering kernel.perf_event_max_sample_rate to 23000
> > > > [57542.266099] perf: interrupt took too long (10940 > 10840), lowering kernel.perf_event_max_sample_rate to 18250
> > > > [57559.645404] perf: interrupt took too long (13714 > 13675), lowering kernel.perf_event_max_sample_rate to 14500
> > > > [61608.697728] Can't find PMC that caused IRQ
> > > > [71774.463111] kmemleak: 12 new suspected memory leaks (see /sys/kernel/debug/kmemleak)
> > > > [92372.044785] process '@/usr/bin/gnatmake-5' started with executable stack
> > > > [92849.380672] FS-Cache: Loaded
> > > > [92849.417269] FS-Cache: Netfs 'nfs' registered for caching
> > > > [92849.595974] NFS: Registering the id_resolver key type
> > > > [92849.596000] Key type id_resolver registered
> > > > [92849.596000] Key type id_legacy registered
> > > > [101808.079143] kmemleak: 1 new suspected memory leaks (see /sys/kernel/debug/kmemleak)
> > > > [106904.323471] Can't find PMC that caused IRQ
> > > > [129416.391456] kmemleak: 1 new suspected memory leaks (see /sys/kernel/debug/kmemleak)
> > > > [158171.604221] kmemleak: 34 new suspected memory leaks (see /sys/kernel/debug/kmemleak)
> > > > $ sudo cat /sys/kernel/debug/kmemleak
> > 
> > When they are no longer present, they are most likely false positives.
> 
> How can this be? Shouldn’t the false positive also be logged in
> `/sys/kernel/debug/kmemleak`?

Sorry, I wasn't clear. It can be a transient false positive. At a
subsequent scan, kmemleak found pointer referring the previously
reported objects and no longer shows them.

> > Was this triggered during boot? Or under some workload?
> 
> From the timestamps it looks like under some load.

Was it during boot? I put a delay of 60s to avoid this but, depending on
the platform, it can still trigger.

-- 
Catalin