From: Miles Chen <miles.chen@xxxxxxxxxxxx>
When slub_debug=O is set. It is possible to clear debug flags
for an "unmergeable" slab cache in kmem_cache_open().
It makes the "unmergeable" cache became "mergeable" in sysfs_slab_add().
These caches will generate their "unique IDs" by create_unique_id(),
but it is possible to create identical unique IDs. In my experiment,
sgpool-128, names_cache, biovec-256 generate the same ID ":Ft-0004096"
and the kernel reports "sysfs: cannot create duplicate filename
'/kernel/slab/:Ft-0004096'".
To repeat my experiment, set disable_higher_order_debug=1,
CONFIG_SLUB_DEBUG_ON=y in kernel-4.14.
Fix this issue by setting unmergeable=1 if slub_debug=O and the
the default slub_debug contains any no-merge flags.
call path:
kmem_cache_create()
__kmem_cache_alias() -> we set SLAB_NEVER_MERGE flags here
create_cache()
__kmem_cache_create()
kmem_cache_open() -> clear DEBUG_METADATA_FLAGS
sysfs_slab_add() -> the slab cache is mergeable now
[ 0.674272] sysfs: cannot create duplicate filename '/kernel/slab/:Ft-0004096'
[ 0.674473] ------------[ cut here ]------------
[ 0.674653] WARNING: CPU: 0 PID: 1 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x60/0x7c
[ 0.674847] Modules linked in:
[ 0.674969] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G W 4.14.0-rc7ajb-00131-gd4c2e9f-dirty #123
[ 0.675211] Hardware name: linux,dummy-virt (DT)
[ 0.675342] task: ffffffc07d4e0080 task.stack: ffffff8008008000
[ 0.675505] PC is at sysfs_warn_dup+0x60/0x7c
[ 0.675633] LR is at sysfs_warn_dup+0x60/0x7c
[ 0.675759] pc : [<ffffff8008235808>] lr : [<ffffff8008235808>] pstate: 60000145
[ 0.675948] sp : ffffff800800bb40
[ 0.676048] x29: ffffff800800bb40 x28: 0000000000000040
[ 0.676209] x27: ffffffc07c52a380 x26: 0000000000000000
[ 0.676369] x25: ffffff8008af4ad0 x24: ffffff8008af4000
[ 0.676528] x23: ffffffc07c532580 x22: ffffffc07cf04598
[ 0.676695] x21: ffffffc07cf26578 x20: ffffffc07c533700
[ 0.676857] x19: ffffffc07ce67000 x18: 0000000000000002
[ 0.677017] x17: 0000000000007ffe x16: 0000000000000007
[ 0.677176] x15: 0000000000000001 x14: 0000000000007fff
[ 0.677335] x13: 0000000000000394 x12: 0000000000000000
[ 0.677492] x11: 00000000000001ab x10: 0000000000000007
[ 0.677651] x9 : 00000000000001ac x8 : ffffff800835d114
[ 0.677809] x7 : 656b2f2720656d61 x6 : 0000000000000017
[ 0.677967] x5 : ffffffc07ffdb9a8 x4 : 0000000000000000
[ 0.678124] x3 : 0000000000000000 x2 : ffffffffffffffff
[ 0.678282] x1 : ffffff8008a4e878 x0 : 0000000000000042
[ 0.678442] Call trace:
[ 0.678528] Exception stack(0xffffff800800ba00 to 0xffffff800800bb40)
[ 0.678706] ba00: 0000000000000042 ffffff8008a4e878 ffffffffffffffff 0000000000000000
[ 0.678914] ba20: 0000000000000000 ffffffc07ffdb9a8 0000000000000017 656b2f2720656d61
[ 0.679121] ba40: ffffff800835d114 00000000000001ac 0000000000000007 00000000000001ab
[ 0.679326] ba60: 0000000000000000 0000000000000394 0000000000007fff 0000000000000001
[ 0.679532] ba80: 0000000000000007 0000000000007ffe 0000000000000002 ffffffc07ce67000
[ 0.679739] baa0: ffffffc07c533700 ffffffc07cf26578 ffffffc07cf04598 ffffffc07c532580
[ 0.679944] bac0: ffffff8008af4000 ffffff8008af4ad0 0000000000000000 ffffffc07c52a380
[ 0.680149] bae0: 0000000000000040 ffffff800800bb40 ffffff8008235808 ffffff800800bb40
[ 0.680354] bb00: ffffff8008235808 0000000060000145 ffffffc07c533700 0000000062616c73
[ 0.680560] bb20: ffffffffffffffff 0000000000000000 ffffff800800bb40 ffffff8008235808
[ 0.680774] [<ffffff8008235808>] sysfs_warn_dup+0x60/0x7c
[ 0.680928] [<ffffff8008235920>] sysfs_create_dir_ns+0x98/0xa0
[ 0.681095] [<ffffff8008539274>] kobject_add_internal+0xa0/0x294
[ 0.681267] [<ffffff80085394f8>] kobject_init_and_add+0x90/0xb4
[ 0.681435] [<ffffff80081b524c>] sysfs_slab_add+0x90/0x200
[ 0.681592] [<ffffff80081b62a0>] __kmem_cache_create+0x26c/0x438
[ 0.681769] [<ffffff80081858a4>] kmem_cache_create+0x164/0x1f4
[ 0.681940] [<ffffff80086caa98>] sg_pool_init+0x60/0x100
[ 0.682094] [<ffffff8008084144>] do_one_initcall+0x38/0x12c
[ 0.682254] [<ffffff80086a0d10>] kernel_init_freeable+0x138/0x1d4
[ 0.682423] [<ffffff8008547388>] kernel_init+0x10/0xfc
[ 0.682571] [<ffffff80080851e0>] ret_from_fork+0x10/0x18
Signed-off-by: Miles Chen <miles.chen@xxxxxxxxxxxx>
---
mm/slub.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/mm/slub.c b/mm/slub.c
index 1efbb812..8e1c027 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5704,6 +5704,10 @@ static int sysfs_slab_add(struct kmem_cache *s)
return 0;
}
+ if (!unmergeable && disable_higher_order_debug &&
+ (slub_debug & DEBUG_METADATA_FLAGS))
+ unmergeable = 1;
+
if (unmergeable) {
/*
* Slabcache can never be merged so we can use the name proper.
--
1.9.1
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