Running z3fold stress testing with address sanitization
showed zhdr->slots was being used after it was freed.
z3fold_free(z3fold_pool, handle)
free_handle(handle)
kmem_cache_free(pool->c_handle, zhdr->slots)
release_z3fold_page_locked_list(kref)
__release_z3fold_page(zhdr, true)
zhdr_to_pool(zhdr)
slots_to_pool(zhdr->slots) *BOOM*
Instead we split free_handle into two functions, release_handle()
and free_slots(). We use release_handle() in place of free_handle(),
and use free_slots() to call kmem_cache_free() after
__release_z3fold_page() is done.
Fixes: 7c2b8baa61fe ("mm/z3fold.c: add structure for buddy handles")
Signed-off-by: Henry Burns <[email protected]>
---
mm/z3fold.c | 33 ++++++++++++++-------------------
1 file changed, 14 insertions(+), 19 deletions(-)
diff --git a/mm/z3fold.c b/mm/z3fold.c
index f7993ff778df..e174d1549734 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -213,31 +213,24 @@ static inline struct z3fold_buddy_slots *handle_to_slots(unsigned long handle)
return (struct z3fold_buddy_slots *)(handle & ~(SLOTS_ALIGN - 1));
}
-static inline void free_handle(unsigned long handle)
+static inline void release_handle(unsigned long handle)
{
- struct z3fold_buddy_slots *slots;
- int i;
- bool is_free;
-
if (handle & (1 << PAGE_HEADLESS))
return;
WARN_ON(*(unsigned long *)handle == 0);
*(unsigned long *)handle = 0;
- slots = handle_to_slots(handle);
- is_free = true;
- for (i = 0; i <= BUDDY_MASK; i++) {
- if (slots->slot[i]) {
- is_free = false;
- break;
- }
- }
+}
- if (is_free) {
- struct z3fold_pool *pool = slots_to_pool(slots);
+/* At this point all of the slots should be empty */
+static inline void free_slots(struct z3fold_buddy_slots *slots)
+{
+ struct z3fold_pool *pool = slots_to_pool(slots);
+ int i;
- kmem_cache_free(pool->c_handle, slots);
- }
+ for (i = 0; i <= BUDDY_MASK; i++)
+ VM_BUG_ON(slots->slot[i]);
+ kmem_cache_free(pool->c_handle, slots);
}
static struct dentry *z3fold_do_mount(struct file_system_type *fs_type,
@@ -431,7 +424,8 @@ static inline struct z3fold_pool *zhdr_to_pool(struct z3fold_header *zhdr)
static void __release_z3fold_page(struct z3fold_header *zhdr, bool locked)
{
struct page *page = virt_to_page(zhdr);
- struct z3fold_pool *pool = zhdr_to_pool(zhdr);
+ struct z3fold_buddy_slots *slots = zhdr->slots;
+ struct z3fold_pool *pool = slots_to_pool(slots);
WARN_ON(!list_empty(&zhdr->buddy));
set_bit(PAGE_STALE, &page->private);
@@ -442,6 +436,7 @@ static void __release_z3fold_page(struct z3fold_header *zhdr, bool locked)
spin_unlock(&pool->lock);
if (locked)
z3fold_page_unlock(zhdr);
+ free_slots(slots);
spin_lock(&pool->stale_lock);
list_add(&zhdr->buddy, &pool->stale);
queue_work(pool->release_wq, &pool->work);
@@ -1009,7 +1004,7 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
return;
}
- free_handle(handle);
+ release_handle(handle);
if (kref_put(&zhdr->refcount, release_z3fold_page_locked_list)) {
atomic64_dec(&pool->pages_nr);
return;
--
2.22.0.410.gd8fdbe21b5-goog
Hi Henry,
On Mon, Jul 1, 2019 at 8:31 PM Henry Burns <[email protected]> wrote:
>
> Running z3fold stress testing with address sanitization
> showed zhdr->slots was being used after it was freed.
>
> z3fold_free(z3fold_pool, handle)
> free_handle(handle)
> kmem_cache_free(pool->c_handle, zhdr->slots)
> release_z3fold_page_locked_list(kref)
> __release_z3fold_page(zhdr, true)
> zhdr_to_pool(zhdr)
> slots_to_pool(zhdr->slots) *BOOM*
Thanks for looking into this. I'm not entirely sure I'm all for
splitting free_handle() but let me think about it.
> Instead we split free_handle into two functions, release_handle()
> and free_slots(). We use release_handle() in place of free_handle(),
> and use free_slots() to call kmem_cache_free() after
> __release_z3fold_page() is done.
A little less intrusive solution would be to move backlink to pool
from slots back to z3fold_header. Looks like it was a bad idea from
the start.
Best regards,
Vitaly
On Tue, Jul 2, 2019 at 12:45 AM Vitaly Wool <[email protected]> wrote:
>
> Hi Henry,
>
> On Mon, Jul 1, 2019 at 8:31 PM Henry Burns <[email protected]> wrote:
> >
> > Running z3fold stress testing with address sanitization
> > showed zhdr->slots was being used after it was freed.
> >
> > z3fold_free(z3fold_pool, handle)
> > free_handle(handle)
> > kmem_cache_free(pool->c_handle, zhdr->slots)
> > release_z3fold_page_locked_list(kref)
> > __release_z3fold_page(zhdr, true)
> > zhdr_to_pool(zhdr)
> > slots_to_pool(zhdr->slots) *BOOM*
>
> Thanks for looking into this. I'm not entirely sure I'm all for
> splitting free_handle() but let me think about it.
>
> > Instead we split free_handle into two functions, release_handle()
> > and free_slots(). We use release_handle() in place of free_handle(),
> > and use free_slots() to call kmem_cache_free() after
> > __release_z3fold_page() is done.
>
> A little less intrusive solution would be to move backlink to pool
> from slots back to z3fold_header. Looks like it was a bad idea from
> the start.
>
> Best regards,
> Vitaly
We still want z3fold pages to be movable though. Wouldn't moving
the backink to the pool from slots to z3fold_header prevent us from
enabling migration?
On Tue, Jul 2, 2019 at 6:57 PM Henry Burns <[email protected]> wrote:
>
> On Tue, Jul 2, 2019 at 12:45 AM Vitaly Wool <[email protected]> wrote:
> >
> > Hi Henry,
> >
> > On Mon, Jul 1, 2019 at 8:31 PM Henry Burns <[email protected]> wrote:
> > >
> > > Running z3fold stress testing with address sanitization
> > > showed zhdr->slots was being used after it was freed.
> > >
> > > z3fold_free(z3fold_pool, handle)
> > > free_handle(handle)
> > > kmem_cache_free(pool->c_handle, zhdr->slots)
> > > release_z3fold_page_locked_list(kref)
> > > __release_z3fold_page(zhdr, true)
> > > zhdr_to_pool(zhdr)
> > > slots_to_pool(zhdr->slots) *BOOM*
> >
> > Thanks for looking into this. I'm not entirely sure I'm all for
> > splitting free_handle() but let me think about it.
> >
> > > Instead we split free_handle into two functions, release_handle()
> > > and free_slots(). We use release_handle() in place of free_handle(),
> > > and use free_slots() to call kmem_cache_free() after
> > > __release_z3fold_page() is done.
> >
> > A little less intrusive solution would be to move backlink to pool
> > from slots back to z3fold_header. Looks like it was a bad idea from
> > the start.
> >
> > Best regards,
> > Vitaly
>
> We still want z3fold pages to be movable though. Wouldn't moving
> the backink to the pool from slots to z3fold_header prevent us from
> enabling migration?
That is a valid point but we can just add back pool pointer to
z3fold_header. The thing here is, there's another patch in the
pipeline that allows for a better (inter-page) compaction and it will
somewhat complicate things, because sometimes slots will have to be
released after z3fold page is released (because they will hold a
handle to another z3fold page). I would prefer that we just added back
pool to z3fold_header and changed zhdr_to_pool to just return
zhdr->pool, then had the compaction patch valid again, and then we
could come back to size optimization.
Best regards,
Vitaly
> > On Tue, Jul 2, 2019 at 12:45 AM Vitaly Wool <[email protected]> wrote:
> > >
> > > Hi Henry,
> > >
> > > On Mon, Jul 1, 2019 at 8:31 PM Henry Burns <[email protected]> wrote:
> > > >
> > > > Running z3fold stress testing with address sanitization
> > > > showed zhdr->slots was being used after it was freed.
> > > >
> > > > z3fold_free(z3fold_pool, handle)
> > > > free_handle(handle)
> > > > kmem_cache_free(pool->c_handle, zhdr->slots)
> > > > release_z3fold_page_locked_list(kref)
> > > > __release_z3fold_page(zhdr, true)
> > > > zhdr_to_pool(zhdr)
> > > > slots_to_pool(zhdr->slots) *BOOM*
> > >
> > > Thanks for looking into this. I'm not entirely sure I'm all for
> > > splitting free_handle() but let me think about it.
> > >
> > > > Instead we split free_handle into two functions, release_handle()
> > > > and free_slots(). We use release_handle() in place of free_handle(),
> > > > and use free_slots() to call kmem_cache_free() after
> > > > __release_z3fold_page() is done.
> > >
> > > A little less intrusive solution would be to move backlink to pool
> > > from slots back to z3fold_header. Looks like it was a bad idea from
> > > the start.
> > >
> > > Best regards,
> > > Vitaly
> >
> > We still want z3fold pages to be movable though. Wouldn't moving
> > the backink to the pool from slots to z3fold_header prevent us from
> > enabling migration?
>
> That is a valid point but we can just add back pool pointer to
> z3fold_header. The thing here is, there's another patch in the
> pipeline that allows for a better (inter-page) compaction and it will
> somewhat complicate things, because sometimes slots will have to be
> released after z3fold page is released (because they will hold a
> handle to another z3fold page). I would prefer that we just added back
> pool to z3fold_header and changed zhdr_to_pool to just return
> zhdr->pool, then had the compaction patch valid again, and then we
> could come back to size optimization.
I see your point, patch incoming.
On Tue, Jul 2, 2019 at 11:03 PM Vitaly Wool <[email protected]> wrote:
>
> On Tue, Jul 2, 2019 at 6:57 PM Henry Burns <[email protected]> wrote:
> >
> > On Tue, Jul 2, 2019 at 12:45 AM Vitaly Wool <[email protected]> wrote:
> > >
> > > Hi Henry,
> > >
> > > On Mon, Jul 1, 2019 at 8:31 PM Henry Burns <[email protected]> wrote:
> > > >
> > > > Running z3fold stress testing with address sanitization
> > > > showed zhdr->slots was being used after it was freed.
> > > >
> > > > z3fold_free(z3fold_pool, handle)
> > > > free_handle(handle)
> > > > kmem_cache_free(pool->c_handle, zhdr->slots)
> > > > release_z3fold_page_locked_list(kref)
> > > > __release_z3fold_page(zhdr, true)
> > > > zhdr_to_pool(zhdr)
> > > > slots_to_pool(zhdr->slots) *BOOM*
> > >
> > > Thanks for looking into this. I'm not entirely sure I'm all for
> > > splitting free_handle() but let me think about it.
> > >
> > > > Instead we split free_handle into two functions, release_handle()
> > > > and free_slots(). We use release_handle() in place of free_handle(),
> > > > and use free_slots() to call kmem_cache_free() after
> > > > __release_z3fold_page() is done.
> > >
> > > A little less intrusive solution would be to move backlink to pool
> > > from slots back to z3fold_header. Looks like it was a bad idea from
> > > the start.
> > >
> > > Best regards,
> > > Vitaly
> >
> > We still want z3fold pages to be movable though. Wouldn't moving
> > the backink to the pool from slots to z3fold_header prevent us from
> > enabling migration?
>
> That is a valid point but we can just add back pool pointer to
> z3fold_header. The thing here is, there's another patch in the
> pipeline that allows for a better (inter-page) compaction and it will
> somewhat complicate things, because sometimes slots will have to be
> released after z3fold page is released (because they will hold a
> handle to another z3fold page). I would prefer that we just added back
> pool to z3fold_header and changed zhdr_to_pool to just return
> zhdr->pool, then had the compaction patch valid again, and then we
> could come back to size optimization.
>
By adding pool pointer back to z3fold_header, will we still be able to
move/migrate/compact the z3fold pages?