On Sat, Jul 22, 2023 at 6:37 PM Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > [ Removed the stable reviewers, bringing in the kfence people ] > > See > > https://lore.kernel.org/lkml/CA+G9fYvgy22wiY=c3wLOrCM6o33636abhtEynXhJkqxJh4ca0A@xxxxxxxxxxxxxx/ > > for the original report. The warning was introduced in 8f0b36497303 > ("mm: kfence: fix objcgs vector allocation"), and Google doesn't find > any other cases of this. > > Anybody? > > Linus > > > NOTE: > > The following kernel warning was noticed while booting qemu-arm64 > > with these configs enabled on stable rc 6.4.5-rc1. > > > > CONFIG_ARM64_64K_PAGES=y > > CONFIG_KFENCE=y Is there a full config somewhere? > > This crash is not easily reproducible. CONFIG_KFENCE_SAMPLE_INTERVAL=10 CONFIG_KFENCE_NUM_OBJECTS=2048 might improve reproducibility. > > > > boot logs: > > -------- > > [ 0.000000] Booting Linux on physical CPU 0x0000000000 [0x000f0510] > > [ 0.000000] Linux version 6.4.5-rc1 (tuxmake@tuxmake) > > (aarch64-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils > > for Debian) 2.40) #1 SMP PREEMPT @1689957802 > > [ 0.000000] random: crng init done > > [ 0.000000] Machine model: linux,dummy-virt > > ... > > [ 0.006821] kfence: initialized - using 33554432 bytes for 255 > > objects at 0x(____ptrval____)-0x(____ptrval____) > > ... > > [ 7.726994] ------------[ cut here ]------------ > > [ 7.727704] WARNING: CPU: 1 PID: 1 at mm/kfence/core.c:1097 > > __kfence_free+0x84/0xc8 > ... > > [ 7.746478] Call trace: > > [ 7.746776] __kfence_free+0x84/0xc8 > > [ 7.747134] __slab_free+0x490/0x508 > > [ 7.748063] __kmem_cache_free+0x2b4/0x2d0 > > [ 7.748377] kfree+0x78/0x140 > > [ 7.748638] single_release+0x40/0x60 > > [ 7.750664] __fput+0x78/0x260 > > [ 7.751065] ____fput+0x18/0x30 > > [ 7.752086] task_work_run+0x80/0xe0 > > [ 7.753122] do_notify_resume+0x200/0x1398 > > [ 7.754292] el0_svc+0xec/0x100 > > [ 7.754573] el0t_64_sync_handler+0xf4/0x120 > > [ 7.755559] el0t_64_sync+0x190/0x198 It would be interesting to see the contents of /sys/kernel/debug/kfence/objects together with the object address. Would it be possible to boot the kernel with no_hash_pointers and add a line printing the object address: diff --git a/mm/kfence/core.c b/mm/kfence/core.c index dad3c0eb70a01..23f27f6cb18cf 100644 --- a/mm/kfence/core.c +++ b/mm/kfence/core.c @@ -1094,7 +1094,10 @@ void __kfence_free(void *addr) struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr); #ifdef CONFIG_MEMCG - KFENCE_WARN_ON(meta->objcg); + if (meta->objcg) { + pr_err("ADDR: %px\n", addr); + KFENCE_WARN_ON(1); + } #endif /* * If the objects of the cache are SLAB_TYPESAFE_BY_RCU, defer freeing , and then dump /sys/kernel/debug/kfence/objects? Knowing the kfence pool location (the line starting with "kfence: initialized") and the object address, we can probably understand from the allocation stack in sysfs, whether the object is supposed to be deleted.
