On 6/15/21 5:58 PM, Qian Cai wrote:
>
>
> On 6/11/2021 3:03 PM, Faiyaz Mohammed wrote:
>> alloc_calls and free_calls implementation in sysfs have two issues,
>> one is PAGE_SIZE limitation of sysfs and other is it does not adhere
>> to "one value per file" rule.
>>
>> To overcome this issues, move the alloc_calls and free_calls
>> implementation to debugfs.
>>
>> Debugfs cache will be created if SLAB_STORE_USER flag is set.
>>
>> Rename the alloc_calls/free_calls to alloc_traces/free_traces,
>> to be inline with what it does.
>>
>> Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
>> Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>> Signed-off-by: Faiyaz Mohammed <faiyazm@xxxxxxxxxxxxxx>
>
> Reverting this commit on today's linux-next fixed all leaks (hundreds) reported by kmemleak like below,
>
> unreferenced object 0xffff00091ae1b540 (size 64):
> comm "lsbug", pid 1607, jiffies 4294958291 (age 1476.340s)
> hex dump (first 32 bytes):
> 02 00 00 00 00 00 00 00 6b 6b 6b 6b 6b 6b 6b 6b ........kkkkkkkk
> 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> backtrace:
> [<ffff8000106b06b8>] slab_post_alloc_hook+0xa0/0x418
> [<ffff8000106b5c7c>] kmem_cache_alloc_trace+0x1e4/0x378
> [<ffff8000106b5e40>] slab_debugfs_start+0x30/0x50
> slab_debugfs_start at /usr/src/linux-next/mm/slub.c:5831
> [<ffff8000107b3dbc>] seq_read_iter+0x214/0xd50
> [<ffff8000107b4b84>] seq_read+0x28c/0x418
> [<ffff8000109560b4>] full_proxy_read+0xdc/0x148
> [<ffff800010738f24>] vfs_read+0x104/0x340
> [<ffff800010739ee0>] ksys_read+0xf8/0x1e0
> [<ffff80001073a03c>] __arm64_sys_read+0x74/0xa8
> [<ffff8000100358d4>] invoke_syscall.constprop.0+0xdc/0x1d8
> [<ffff800010035ab4>] do_el0_svc+0xe4/0x298
> [<ffff800011138528>] el0_svc+0x20/0x30
> [<ffff800011138b08>] el0t_64_sync_handler+0xb0/0xb8
> [<ffff80001001259c>] el0t_64_sync+0x178/0x17c
>
I think the problem is here:
>> +static void slab_debugfs_stop(struct seq_file *seq, void *v)
>> +{
>> + kfree(v);
>> +}
>> +
>> +static void *slab_debugfs_next(struct seq_file *seq, void *v, loff_t *ppos)
>> +{
>> + loff_t *spos = v;
>> + struct loc_track *t = seq->private;
>> +
>> + if (*ppos < t->count) {
>> + *ppos = ++*spos;
>> + return spos;
>> + }
>> + *ppos = ++*spos;
>> + return NULL;
>> +}
If we return NULL, then NULL is passed to slab_debugfs_stop and thus we don't
kfree ppos. kfree(NULL) is silently ignored.
I think as we have private struct loc_track, we can add a pos field there and
avoid the kmaloc/kfree altogether.
