On Fri, 2022-06-24 at 10:28 +0200, Marco Elver wrote:
On Fri, 24 Jun 2022 at 10:20, 'Yee Lee' via kasan-dev
On Thu, 2022-06-23 at 13:59 +0200, Marco Elver wrote:
On Thu, 23 Jun 2022 at 13:20, yee.lee via kasan-dev
Use MEMBLOCK_ALLOC_NOLEAKTRACE to skip kmemleak registration when
the kfence pool is allocated from memblock. And the kmemleak_free
later can be removed too.
Is this purely meant to be a cleanup and non-functional change?
---
mm/kfence/core.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)
diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 4e7cd4c8e687..0d33d83f5244 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -600,14 +600,6 @@ static unsigned long kfence_init_pool(void)
addr += 2 * PAGE_SIZE;
}
- /*
- * The pool is live and will never be deallocated from this
point on.
- * Remove the pool object from the kmemleak object tree, as
it would
- * otherwise overlap with allocations returned by
kfence_alloc(), which
- * are registered with kmemleak through the slab post-alloc
hook.
- */
- kmemleak_free(__kfence_pool);
This appears to only be a non-functional change if the pool is
allocated early. If the pool is allocated late using page-alloc, then
there'll not be a kmemleak_free() on that memory and we'll have the
same problem.
Do you mean the kzalloc(slab_is_available) in memblock_allc()? That
implies that MEMBLOCK_ALLOC_NOLEAKTRACE has no guarantee skipping
kmemleak_alloc from this. (Maybe add it?)
No, if KFENCE is initialized through kfence_init_late() ->
kfence_init_pool_late() -> kfence_init_pool().
Thanks for the information.
But as I known, page-alloc does not request kmemleak areas.
So the current kfence_pool_init_late() would cause another kmemleak warning on unknown freeing.
Reproducing test: (kfence late enable + kmemleak debug on)
/ # echo 500 > /sys/module/kfence/parameters/sample_interval
[ 153.433518] kmemleak: Freeing unknown object at 0xffff0000c0600000
[ 153.433804] CPU: 0 PID: 100 Comm: sh Not tainted 5.19.0-rc3-74069-gde5c208d533a-dirty #1
[ 153.434027] Hardware name: linux,dummy-virt (DT)
[ 153.434265] Call trace:
[ 153.434331] dump_backtrace+0xdc/0xfc
[ 153.434962] show_stack+0x18/0x24
[ 153.435106] dump_stack_lvl+0x64/0x7c
[ 153.435232] dump_stack+0x18/0x38
[ 153.435347] kmemleak_free+0x184/0x1c8
[ 153.435462] kfence_init_pool+0x16c/0x194
[ 153.435587] param_set_sample_interval+0xe0/0x1c4
[ 153.435694] param_attr_store+0x98/0xf4
[ 153.435804] module_attr_store+0x24/0x3c
[ 153.435910] sysfs_kf_write+0x3c/0x50
...(skip)
[ 153.444496] kfence: initialized - using 524288 bytes for 63 objects at 0x00000000a3236b01-0x00000000901655d3
/ #
Hence, now there are two issues to solve.
(1) (The original)To prevent the undesired kmemleak scanning on the kfence pool. As Cataline's suggestion, we can just apply kmemleak_ignore_phys instead of free it at all.
(2) The late-allocated kfence pool doesn't need to go through kmemleak_free. We can relocate the opeartion to kfence_init_pool_early() to seperate them.
That is, kfence_init_pool_early(memblock) has it and kfence_init_pool_late(page alloc) does not.
The draft is like the following.
diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 11a954763be9..a52db7f06c04 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -591,14 +591,6 @@ static unsigned long kfence_init_pool(void)
addr += 2 * PAGE_SIZE;
}
- /*
- * The pool is live and will never be deallocated from this point on.
- * Remove the pool object from the kmemleak object tree, as it would
- * otherwise overlap with allocations returned by kfence_alloc(), which
- * are registered with kmemleak through the slab post-alloc hook.
- */
- kmemleak_free(__kfence_pool);
-
return 0;
}
@@ -611,8 +603,16 @@ static bool __init kfence_init_pool_early(void)
addr = kfence_init_pool();
- if (!addr)
+ if (!addr) {
+ /*
+ * The pool is live and will never be deallocated from this point on.
+ * Ignore the pool object from the kmemleak phys object tree, as it would
+ * otherwise overlap with allocations returned by kfence_alloc(), which
+ * are registered with kmemleak through the slab post-alloc hook.
+ */
+ kmemleak_ignore_phys(__pa(__kfence_pool));
return true;
+ }
/*
* Only release unprotected pages, and do not try to go back and change