linux-kernel - Re: [PATCH mm-stable] uprobes: Revert ref_ctr_offset in uprobe

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Message-ID: <e1d01068-238c-4fe3-98ce-5c44753b321f@redhat.com>
Date: Tue, 13 May 2025 18:56:59 +0200
From: David Hildenbrand <david@...hat.com>
To: Oleg Nesterov <oleg@...hat.com>, Jiri Olsa <jolsa@...nel.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, Andrii Nakryiko <andrii@...nel.org>,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH mm-stable] uprobes: Revert ref_ctr_offset in
 uprobe_unregister error path

On 13.05.25 17:46, Oleg Nesterov wrote:
> On 05/13, Jiri Olsa wrote:
>>
>> --- a/kernel/events/uprobes.c
>> +++ b/kernel/events/uprobes.c
>> @@ -581,8 +581,8 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
>>   
>>   out:
>>   	/* Revert back reference counter if instruction update failed. */
>> -	if (ret < 0 && is_register && ref_ctr_updated)
>> -		update_ref_ctr(uprobe, mm, -1);
>> +	if (ret < 0 && ref_ctr_updated)
>> +		update_ref_ctr(uprobe, mm, is_register ? -1 : 1);
> 
> Acked-by: Oleg Nesterov <oleg@...hat.com>
> 
> And just in case, I agree this has nothing to do with the recent changes from David.

BTW, I stumbled over this when doing the rework.

Back then, I was wondering if this is to handle the case where 
un-registering effectively fails because someone MADV_DONTNEED'ed the page.

But, we only perform the update_ref_ctr() after verify_opcode(), so that 
does not apply.

With proper Fixes:

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb