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 > wrote: > > > > 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 > > > wrote: > > > > > > > > From: Yee Lee > > > > > > > > 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? > > > > > > > Signed-off-by: Yee Lee > > > > > > > > --- > > > > 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. ref: https://lore.kernel.org/linux-mm/YrWPg3xIHbm9bFxP@arm.com/ (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