The patch titled Subject: mm: kmem: properly initialize local objcg variable in current_obj_cgroup() has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-kmem-properly-initialize-local-objcg-variable-in-current_obj_cgroup.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-kmem-properly-initialize-local-objcg-variable-in-current_obj_cgroup.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Roman Gushchin <roman.gushchin@xxxxxxxxx> Subject: mm: kmem: properly initialize local objcg variable in current_obj_cgroup() Date: Wed, 15 Nov 2023 18:51:09 -0800 Erhard reported that the 6.7-rc1 kernel panics on boot if being built with clang-16. The problem was not reproducible with gcc. [ 5.975049] general protection fault, probably for non-canonical address 0xf555515555555557: 0000 [#1] SMP KASAN PTI [ 5.976422] KASAN: maybe wild-memory-access in range [0xaaaaaaaaaaaaaab8-0xaaaaaaaaaaaaaabf] [ 5.977475] CPU: 3 PID: 1 Comm: systemd Not tainted 6.7.0-rc1-Zen3 #77 [ 5.977860] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014 [ 5.977860] RIP: 0010:obj_cgroup_charge_pages+0x27/0x2d5 [ 5.977860] Code: 90 90 90 55 41 57 41 56 41 55 41 54 53 89 d5 41 89 f6 49 89 ff 48 b8 00 00 00 00 00 fc ff df 49 83 c7 10 4d3 [ 5.977860] RSP: 0018:ffffc9000001fb18 EFLAGS: 00010a02 [ 5.977860] RAX: dffffc0000000000 RBX: aaaaaaaaaaaaaaaa RCX: ffff8883eb9a8b08 [ 5.977860] RDX: 0000000000000005 RSI: 0000000000400cc0 RDI: aaaaaaaaaaaaaaaa [ 5.977860] RBP: 0000000000000005 R08: 3333333333333333 R09: 0000000000000000 [ 5.977860] R10: 0000000000000000 R11: 0000000000000000 R12: ffff8883eb9a8b18 [ 5.977860] R13: 1555555555555557 R14: 0000000000400cc0 R15: aaaaaaaaaaaaaaba [ 5.977860] FS: 00007f2976438b40(0000) GS:ffff8883eb980000(0000) knlGS:0000000000000000 [ 5.977860] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 5.977860] CR2: 00007f29769e0060 CR3: 0000000107222003 CR4: 0000000000370eb0 [ 5.977860] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 5.977860] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 5.977860] Call Trace: [ 5.977860] <TASK> [ 5.977860] ? __die_body+0x16/0x75 [ 5.977860] ? die_addr+0x4a/0x70 [ 5.977860] ? exc_general_protection+0x1c9/0x2d0 [ 5.977860] ? cgroup_mkdir+0x455/0x9fb [ 5.977860] ? __x64_sys_mkdir+0x69/0x80 [ 5.977860] ? asm_exc_general_protection+0x26/0x30 [ 5.977860] ? obj_cgroup_charge_pages+0x27/0x2d5 [ 5.977860] obj_cgroup_charge+0x114/0x1ab [ 5.977860] pcpu_alloc+0x1a6/0xa65 [ 5.977860] ? mem_cgroup_css_alloc+0x1eb/0x1140 [ 5.977860] ? cgroup_apply_control_enable+0x26b/0x7c0 [ 5.977860] mem_cgroup_css_alloc+0x23f/0x1140 [ 5.977860] cgroup_apply_control_enable+0x26b/0x7c0 [ 5.977860] ? cgroup_kn_set_ugid+0x2d/0x1a0 [ 5.977860] cgroup_mkdir+0x455/0x9fb [ 5.977860] ? __cfi_cgroup_mkdir+0x10/0x10 [ 5.977860] kernfs_iop_mkdir+0x130/0x170 [ 5.977860] vfs_mkdir+0x405/0x530 [ 5.977860] do_mkdirat+0x188/0x1f0 [ 5.977860] __x64_sys_mkdir+0x69/0x80 [ 5.977860] do_syscall_64+0x7d/0x100 [ 5.977860] ? do_syscall_64+0x89/0x100 [ 5.977860] ? do_syscall_64+0x89/0x100 [ 5.977860] ? do_syscall_64+0x89/0x100 [ 5.977860] ? do_syscall_64+0x89/0x100 [ 5.977860] entry_SYSCALL_64_after_hwframe+0x4b/0x53 [ 5.977860] RIP: 0033:0x7f297671defb [ 5.977860] Code: 8b 05 39 7f 0d 00 bb ff ff ff ff 64 c7 00 16 00 00 00 e9 61 ff ff ff e8 23 0c 02 00 0f 1f 00 f3 0f 1e fa b88 [ 5.977860] RSP: 002b:00007ffee6242bb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000053 [ 5.977860] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f297671defb [ 5.977860] RDX: 0000000000000000 RSI: 00000000000001ed RDI: 000055c6b449f0e0 [ 5.977860] RBP: 00007ffee6242bf0 R08: 000000000000000e R09: 0000000000000000 [ 5.977860] R10: 0000000000000000 R11: 0000000000000246 R12: 000055c6b445db80 [ 5.977860] R13: 00000000000003a0 R14: 00007f2976a68651 R15: 00000000000003a0 [ 5.977860] </TASK> [ 5.977860] Modules linked in: [ 6.014095] ---[ end trace 0000000000000000 ]--- [ 6.014701] RIP: 0010:obj_cgroup_charge_pages+0x27/0x2d5 [ 6.015348] Code: 90 90 90 55 41 57 41 56 41 55 41 54 53 89 d5 41 89 f6 49 89 ff 48 b8 00 00 00 00 00 fc ff df 49 83 c7 10 4d3 [ 6.017575] RSP: 0018:ffffc9000001fb18 EFLAGS: 00010a02 [ 6.018255] RAX: dffffc0000000000 RBX: aaaaaaaaaaaaaaaa RCX: ffff8883eb9a8b08 [ 6.019120] RDX: 0000000000000005 RSI: 0000000000400cc0 RDI: aaaaaaaaaaaaaaaa [ 6.019983] RBP: 0000000000000005 R08: 3333333333333333 R09: 0000000000000000 [ 6.020849] R10: 0000000000000000 R11: 0000000000000000 R12: ffff8883eb9a8b18 [ 6.021747] R13: 1555555555555557 R14: 0000000000400cc0 R15: aaaaaaaaaaaaaaba [ 6.022609] FS: 00007f2976438b40(0000) GS:ffff8883eb980000(0000) knlGS:0000000000000000 [ 6.023593] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 6.024296] CR2: 00007f29769e0060 CR3: 0000000107222003 CR4: 0000000000370eb0 [ 6.025279] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 6.026139] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 6.027000] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b Actually the problem is caused by uninitialized local variable in current_obj_cgroup(). If the root memory cgroup is set as an active memory cgroup for a charging scope (as in the trace, where systemd tries to create the first non-root cgroup, so the parent cgroup is the root cgroup), the "for" loop is skipped and uninitialized objcg is returned, causing a panic down the accounting stack. The fix is trivial: initialize the objcg variable to NULL unconditionally before the "for" loop. Link: https://lkml.kernel.org/r/20231116025109.3775055-1-roman.gushchin@xxxxxxxxx Fixes: e86828e5446d ("mm: kmem: scoped objcg protection") Reported-by: Erhard Furtner <erhard_f@xxxxxxxxxxx> Closes: https://github.com/ClangBuiltLinux/linux/issues/1959 Signed-off-by: Roman Gushchin (Cruise) <roman.gushchin@xxxxxxxxx> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Dennis Zhou <dennis@xxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Muchun Song <muchun.song@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/memcontrol.c | 1 + 1 file changed, 1 insertion(+) --- a/mm/memcontrol.c~mm-kmem-properly-initialize-local-objcg-variable-in-current_obj_cgroup +++ a/mm/memcontrol.c @@ -3166,6 +3166,7 @@ __always_inline struct obj_cgroup *curre return NULL; from_memcg: + objcg = NULL; for (; !mem_cgroup_is_root(memcg); memcg = parent_mem_cgroup(memcg)) { /* * Memcg pointer is protected by scope (see set_active_memcg()) _ Patches currently in -mm which might be from roman.gushchin@xxxxxxxxx are mm-kmem-properly-initialize-local-objcg-variable-in-current_obj_cgroup.patch