| Message ID | 20190925143912.22593-1-apw@canonical.com (mailing list archive) |
|---|---|
| State | Mainlined, archived |
| Headers | show |
| Series | [1/1] PM / hibernate: memory_bm_find_bit -- tighten node optimisation | expand |
On Wednesday, September 25, 2019 4:39:12 PM CEST Andy Whitcroft wrote: > When looking for a bit by number we make use of the cached result from the > preceding lookup to speed up operation. Firstly we check if the requested > pfn is within the cached zone and if not lookup the new zone. We then > check if the offset for that pfn falls within the existing cached node. > This happens regardless of whether the node is within the zone we are > now scanning. With certain memory layouts it is possible for this to > false trigger creating a temporary alias for the pfn to a different bit. > This leads the hibernation code to free memory which it was never allocated > with the expected fallout. > > Ensure the zone we are scanning matches the cached zone before considering > the cached node. > > Deep thanks go to Andrea for many, many, many hours of hacking and testing > that went into cornering this bug. > > Reported-by: Andrea Righi <andrea.righi@canonical.com> > Tested-by: Andrea Righi <andrea.righi@canonical.com> > Signed-off-by: Andy Whitcroft <apw@canonical.com> > --- > kernel/power/snapshot.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c > index 83105874f255..26b9168321e7 100644 > --- a/kernel/power/snapshot.c > +++ b/kernel/power/snapshot.c > @@ -734,8 +734,15 @@ static int memory_bm_find_bit(struct memory_bitmap *bm, unsigned long pfn, > * We have found the zone. Now walk the radix tree to find the leaf node > * for our PFN. > */ > + > + /* > + * If the zone we wish to scan is the the current zone and the > + * pfn falls into the current node then we do not need to walk > + * the tree. > + */ > node = bm->cur.node; > - if (((pfn - zone->start_pfn) & ~BM_BLOCK_MASK) == bm->cur.node_pfn) > + if (zone == bm->cur.zone && > + ((pfn - zone->start_pfn) & ~BM_BLOCK_MASK) == bm->cur.node_pfn) > goto node_found; > > node = zone->rtree; > Applying as 5.5 material, thanks!
diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c index 83105874f255..26b9168321e7 100644 --- a/kernel/power/snapshot.c +++ b/kernel/power/snapshot.c @@ -734,8 +734,15 @@ static int memory_bm_find_bit(struct memory_bitmap *bm, unsigned long pfn, * We have found the zone. Now walk the radix tree to find the leaf node * for our PFN. */ + + /* + * If the zone we wish to scan is the the current zone and the + * pfn falls into the current node then we do not need to walk + * the tree. + */ node = bm->cur.node; - if (((pfn - zone->start_pfn) & ~BM_BLOCK_MASK) == bm->cur.node_pfn) + if (zone == bm->cur.zone && + ((pfn - zone->start_pfn) & ~BM_BLOCK_MASK) == bm->cur.node_pfn) goto node_found; node = zone->rtree;