There is a way to write a test for descriptor leaks, and I'd be willing to take a crack at it; could the original poster respond to me directly with some problematic code?Note: I'm relatively unfamiliar with the code base these days, so it may take me a little time to get up to speed on how tests are set up.Regards,Tom Dial
From: Nick Mathewson <nickm@xxxxxxxxxxxxx>
To: libevent-users@xxxxxxxxxxxxx
Sent: Tuesday, July 30, 2013 8:46 AM
Subject: Re: [Libevent-users] Fwd: leaking munmap
On Tue, Jul 30, 2013 at 1:48 AM, Black Hole <randomblackhole@xxxxxxxxx> wrote:
>
>
> ---------- Forwarded message ----------
> From: Black Hole <randomblackhole@xxxxxxxxx>
> Date: Tue, Jul 30, 2013 at 3:46 PM
> Subject: leaking munmap
> To: majordomo@xxxxxxxx
>
>
> Using 2.1-alpha.
>
> In evbuffer_file_segment_free, buffer.c:3077
>
> I think the line:
>
> if (munmap(seg->mapping, seg->length) == -1)
>
> should read:
>
> off_t offset_leftover = seg->file_offset & (page_size - 1);
>
> if (munmap(seg->mapping, seg->length + offset_leftover) == -1)
>
>
> Without that change, it would leak memory and kernel descriptors.
Hm. Seems plausible; I wonder if there's a way to write a test for this.
> On a related note, would there be any benefit in caching the pagesize
> instead of calling sysconf() each time? Something like:
>>
>> /* pagesize should be a power of 2 */
>> long getpagesize_(void) {
>> static long page_size = -2;
>> if (page_size == -2) {
>> #ifdef SC_PAGE_SIZE
>> page_size = sysconf(SC_PAGE_SIZE);
>> #elif defined(_SC_PAGE_SIZE)
>> page_size = sysconf(_SC_PAGE_SIZE);
>> #else
>> page_size = 4096;
>> #endif
>> }
>> return page_size;
>> }
Is there a platform where sysconf is slow or expensive? My
understanding is that it's usually (always?) a libc function, not a
syscall, and it should run pretty fast.
> Also, in evbuffer_file_segment_materialize() around line 2980, the
> calculation of "offset_leftover" we can remove the modulus in favour of a
> mask.
>>
>> long page_size = getpagesize_();
>>
>> if (page_size == -1)
>>
>> goto err;
>>
>> offset_leftover = offset & (page_size - 1);
Assuming that the page size is always a power of 2, yeah. (I'm not
aware of any systems pathological enough to have 6K pages or
something, so this should be fine.)
--
Nick
***********************************************************************
To unsubscribe, send an e-mail to majordomo@xxxxxxxxxxxxx with
unsubscribe libevent-users in the body.