From: Yazen Ghannam yazen.ghannam@amd.com
commit 3ba2e83334bed2b1980b59734e6e84dfaf96026c upstream.
AMD systems from Family 10h to 16h share MCA bank 4 across multiple CPUs. Therefore, the threshold_bank structure for bank 4, and its threshold_block structures, will be initialized once at boot time. And the kobject for the shared bank will be added to each of the CPUs that share it. Furthermore, the threshold_blocks for the shared bank will be added again to the bank's kobject. These additions will increase the refcount for the bank's kobject.
For example, a shared bank with two blocks and shared across two CPUs will be set up like this:
CPU0 init bank create and add; bank refcount = 1; threshold_create_bank() block 0 init and add; bank refcount = 2; allocate_threshold_blocks() block 1 init and add; bank refcount = 3; allocate_threshold_blocks() CPU1 init bank add; bank refcount = 3; threshold_create_bank() block 0 add; bank refcount = 4; __threshold_add_blocks() block 1 add; bank refcount = 5; __threshold_add_blocks()
Currently in threshold_remove_bank(), if the bank is shared then __threshold_remove_blocks() is called. Here the shared bank's kobject and the bank's blocks' kobjects are deleted. This is done on the first call even while the structures are still shared. Subsequent calls from other CPUs that share the structures will attempt to delete the kobjects.
During kobject_del(), kobject->sd is removed. If the kobject is not part of a kset with default_groups, then subsequent kobject_del() calls seem safe even with kobject->sd == NULL.
Originally, the AMD MCA thresholding structures did not use default_groups. And so the above behavior was not apparent.
However, a recent change implemented default_groups for the thresholding structures. Therefore, kobject_del() will go down the sysfs_remove_groups() code path. In this case, the first kobject_del() may succeed and remove kobject->sd. But subsequent kobject_del() calls will give a WARNing in kernfs_remove_by_name_ns() since kobject->sd == NULL.
Use kobject_put() on the shared bank's kobject when "removing" blocks. This decrements the bank's refcount while keeping kobjects enabled until the bank is no longer shared. At that point, kobject_put() will be called on the blocks which drives their refcount to 0 and deletes them and also decrementing the bank's refcount. And finally kobject_put() will be called on the bank driving its refcount to 0 and deleting it.
The same example above:
CPU1 shutdown bank is shared; bank refcount = 5; threshold_remove_bank() block 0 put parent bank; bank refcount = 4; __threshold_remove_blocks() block 1 put parent bank; bank refcount = 3; __threshold_remove_blocks() CPU0 shutdown bank is no longer shared; bank refcount = 3; threshold_remove_bank() block 0 put block; bank refcount = 2; deallocate_threshold_blocks() block 1 put block; bank refcount = 1; deallocate_threshold_blocks() put bank; bank refcount = 0; threshold_remove_bank()
Fixes: 7f99cb5e6039 ("x86/CPU/AMD: Use default_groups in kobj_type") Reported-by: Mikulas Patocka mpatocka@redhat.com Signed-off-by: Yazen Ghannam yazen.ghannam@amd.com Signed-off-by: Borislav Petkov (AMD) bp@alien8.de Tested-by: Mikulas Patocka mpatocka@redhat.com Cc: stable@kernel.org Link: https://lore.kernel.org/r/alpine.LRH.2.02.2205301145540.25840@file01.intrane... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kernel/cpu/mce/amd.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/arch/x86/kernel/cpu/mce/amd.c +++ b/arch/x86/kernel/cpu/mce/amd.c @@ -1265,10 +1265,10 @@ static void __threshold_remove_blocks(st struct threshold_block *pos = NULL; struct threshold_block *tmp = NULL;
- kobject_del(b->kobj); + kobject_put(b->kobj);
list_for_each_entry_safe(pos, tmp, &b->blocks->miscj, miscj) - kobject_del(&pos->kobj); + kobject_put(b->kobj); }
static void threshold_remove_bank(struct threshold_bank *bank)