Re: [RFC PATCH v1 15/25] unwind_user/eh_frame: Duplicate registered .eh_frame[_hdr] section data on clone/fork

[Jens Remus <jremus@linux.ibm.com>]

On 8/18/2026 5:11 PM, sashiko-bot@kernel.org wrote:

> This commit ensures that a process's registered .eh_frame_hdr sections are
> duplicated in the per-mm maple tree during virtual memory duplication. This
> enables stack tracing for child processes using eh_frame.

>> diff --git a/kernel/unwind/eh_frame.c b/kernel/unwind/eh_frame.c

>> +int eh_frame_dup_mm(struct mm_struct *mm, struct mm_struct *oldmm)
>> +{
>> +	struct eh_frame_section *sec, *oldsec;
>> +	unsigned long index = 0;
>> +	int ret;
>> +
>> +	guard(srcu)(&eh_frame_srcu);
>> +
>> +	mt_for_each(&oldmm->eh_frame_mt, oldsec, index, ULONG_MAX) {
>> +		sec = kzalloc(sizeof(*sec), GFP_KERNEL_ACCOUNT);
>> +		if (!sec)
>> +			return -ENOMEM;
>> +
>> +		__eh_frame_dup_section(sec, oldsec);
>> +
>> +		ret = mtree_insert_range(&mm->eh_frame_mt,
>> +					 sec->text_start,
>> +					 sec->text_end - 1,
>> +					 sec, GFP_KERNEL_ACCOUNT);
>> +		if (ret)
>> +			goto err_free;
>> +	}
>> +
>> +	return 0;
>> +
>> +err_free:
>> +	free_section(sec);
>> +	return ret;
>> +}
> 
> [Severity: Low]
> This isn't a bug, but does this function mix scope-based cleanup with
> traditional goto-based error handling?

No.  The guard(srcu)(&eh_frame_srcu) is for read access of the oldsec
obtained from the oldmm->eh_frame_mt.  The goto-based error handling
is for the new copy sec, in case inserting into mm->eh_frame_mt failed.

> 
> The kernel's cleanup guidelines specify that usage of goto and cleanup
> helpers like guard() should not be mixed in the same function. Could this
> be converted to use scope-based cleanup entirely, or avoid guard() to keep
> the style consistent?
Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
jremus@de.ibm.com / jremus@linux.ibm.com

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