Mergeable slab can be changed to unmergeable after tuning its sysfs
interface, for example echo 1 > trace. But the sysfs kobject with the unique
name will be still there.
When creating a new mergeable slab, the following warning will happen:
(hello.ko is a trivial module to simply create a mergeable slab)
[ 408.915029] ------------[ cut here ]------------
[ 408.919641] WARNING: CPU: 3 PID: 2766 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x64/0x80()
[ 408.927449] sysfs: cannot create duplicate filename '/kernel/slab/:t-0000048'
[ 408.934563] Modules linked in: hello(O+) ipt_MASQUERADE iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack xt_CHECKSUM iptable_mangle tun bridge stpi
[ 408.980823] CPU: 3 PID: 2766 Comm: modprobe Tainted: G O 3.17.0-rc1 #22
[ 408.988981] Hardware name: Dell Inc. OptiPlex 760 /0M860N, BIOS A12 05/23/2011
[ 408.997571] 0000000000000009 ffff8801a053ba40 ffffffff816c560e ffff8801a053ba88
[ 409.004994] ffff8801a053ba78 ffffffff810bbb2d ffff8800b6b6d000 ffff8800b65bc580
[ 409.012414] ffff8801a04260f0 0000000000000000 ffff880035d58b78 ffff8801a053bad8
[ 409.019839] Call Trace:
[ 409.022290] [<ffffffff816c560e>] dump_stack+0x45/0x56
[ 409.027418] [<ffffffff810bbb2d>] warn_slowpath_common+0x7d/0xa0
[ 409.033415] [<ffffffff810bbb9c>] warn_slowpath_fmt+0x4c/0x50
[ 409.039156] [<ffffffff81273588>] ? kernfs_path+0x48/0x60
[ 409.044546] [<ffffffff81276bd4>] sysfs_warn_dup+0x64/0x80
[ 409.050027] [<ffffffff81276c7e>] sysfs_create_dir_ns+0x8e/0xa0
[ 409.055938] [<ffffffff81362f2f>] kobject_add_internal+0xbf/0x3f0
[ 409.062019] [<ffffffff81363610>] kobject_init_and_add+0x60/0x80
[ 409.068016] [<ffffffff811f2836>] ? sysfs_slab_add+0x146/0x200
[ 409.073845] [<ffffffff811f2771>] sysfs_slab_add+0x81/0x200
[ 409.079409] [<ffffffff811f518b>] __kmem_cache_create+0x51b/0x860
[ 409.085494] [<ffffffffc0094000>] ? 0xffffffffc0094000
[ 409.090627] [<ffffffff816c22ef>] ? printk+0x67/0x69
[ 409.095584] [<ffffffff811f45d2>] ? kmem_cache_alloc+0x1c2/0x1f0
[ 409.101581] [<ffffffff811bf3bb>] ? do_kmem_cache_create+0x3b/0xf0
[ 409.107752] [<ffffffff811bf42b>] do_kmem_cache_create+0xab/0xf0
[ 409.113749] [<ffffffff811bf622>] kmem_cache_create+0x1b2/0x2a0
[ 409.119661] [<ffffffff8136fa5e>] ? kasprintf+0x3e/0x40
[ 409.124881] [<ffffffffc0094000>] ? 0xffffffffc0094000
[ 409.130019] [<ffffffffc009403a>] init_hello+0x3a/0x1000 [hello]
[ 409.136019] [<ffffffff8100212c>] do_one_initcall+0xbc/0x1f0
[ 409.141671] [<ffffffff811da2c2>] ? __vunmap+0xb2/0x100
[ 409.146891] [<ffffffff8112e12e>] load_module+0x1e4e/0x25e0
[ 409.152455] [<ffffffff81129f40>] ? store_uevent+0x40/0x40
[ 409.157934] [<ffffffff8112aa31>] ? copy_module_from_fd.isra.47+0x121/0x180
[ 409.164884] [<ffffffff8112ea36>] SyS_finit_module+0x86/0xb0
[ 409.170539] [<ffffffff816cbba9>] system_call_fastpath+0x16/0x1b
[ 409.176533] ---[ end trace c8eef8076cd27e36 ]---
Now if a unique is taken, we suffix it with an index, for example,
/sys/kernel/slab/:t-0000048 is already there, but not mergeable. We create
another unique name with index suffix, /sys/kernel/slab/:t-0000048-1, if
this one is taken too, we increase the index value each time, :t-0000048-2,
:t-0000048-3 ... until we find one.
Signed-off-by: WANG Chao <chaowang@xxxxxxxxxx>
---
mm/slub.c | 34 ++++++++++++++++++++++++++++++++--
1 file changed, 32 insertions(+), 2 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index 3e8afcc..8b4944e 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5099,9 +5099,9 @@ static inline struct kset *cache_kset(struct kmem_cache *s)
/* Create a unique string id for a slab cache:
*
- * Format :[flags-]size
+ * Format :[flags-]size[-index]
*/
-static char *create_unique_id(struct kmem_cache *s)
+static char *__create_unique_id(struct kmem_cache *s, int index)
{
char *name = kmalloc(ID_STR_LENGTH, GFP_KERNEL);
char *p = name;
@@ -5127,11 +5127,41 @@ static char *create_unique_id(struct kmem_cache *s)
if (p != name + 1)
*p++ = '-';
p += sprintf(p, "%07d", s->size);
+ if (index)
+ p += sprintf(p, "-%d", index);
BUG_ON(p > name + ID_STR_LENGTH - 1);
return name;
}
+static char *create_unique_id(struct kmem_cache *s)
+{
+ char *name;
+ struct kmem_cache *k;
+ int index, unique;
+
+
+ for (index = 0, unique = 0; !unique; index++) {
+ name = __create_unique_id(s, index);
+ unique = 1;
+
+ /*
+ * Walk through slab_caches to see if name is taken.
+ * It happens when mergeables becomes unmergeables.
+ */
+ list_for_each_entry(k, &slab_caches, list) {
+ if (!k->kobj.name)
+ continue;
+
+ if (!strcmp(k->kobj.name, name)) {
+ unique = 0;
+ break;
+ }
+ }
+ }
+ return name;
+}
+
static int sysfs_slab_add(struct kmem_cache *s)
{
int err;
--
1.9.3
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