On 2017-08-31 21:11:08 [+0200], Thomas Gleixner wrote: > On Wed, 23 Aug 2017, Mike Galbraith wrote: > > > > > Use get_local_ptr() vs this_cpu_ptr(). > > > > Signed-off-by: Mike Galbraith <[email protected]> > > --- > > drivers/block/zram/zcomp.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > --- a/drivers/block/zram/zcomp.c > > +++ b/drivers/block/zram/zcomp.c > > @@ -120,7 +120,7 @@ struct zcomp_strm *zcomp_stream_get(stru > > { > > struct zcomp_strm *zstrm; > > > > - zstrm = *this_cpu_ptr(comp->stream); > > + zstrm = *get_local_ptr(comp->stream); > > This looks wrong. On mainline the calling code must have preemption disable > somehow, otherwise this_cpu_ptr() would not work.
This was introduced by Mike in a previous patch. The zstrm is only accessed while the spinlock is held. > Looking at the call site it is; > > zram_slot_lock() > bit_spin_lock() > > which is of course evading lockdep and everything else debugging wise. > > Sebastian, do we have migration protection in bitlocked regions? And we > shpuld look into converting that into a spinlock on rt. zram_lock_table() is bit_spin_lock() on !RT and spin_lock(&table->lock); on RT. So this is done. !RT has this running in a kmap_atomic() section so they have no preemption there. zcomp_stream_get() returns a per-CPU object which is protected with a spinlock and only accessed locked. > Thanks, > > tglx Sebastian
