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Re: Question about madvise(DONTNEED) in glibc malloc
- From: OndÅej BÃlka <neleai at seznam dot cz>
- To: Rich Felker <dalias at aerifal dot cx>
- Cc: Samuel Thibault <samuel dot thibault at ens-lyon dot org>, KOSAKI Motohiro <kosaki dot motohiro at gmail dot com>, Siddhesh Poyarekar <siddhesh dot poyarekar at gmail dot com>, libc-alpha <libc-alpha at sourceware dot org>
- Date: Mon, 15 Apr 2013 15:04:39 +0200
- Subject: Re: Question about madvise(DONTNEED) in glibc malloc
- References: <516ADB3C dot 9040805 at gmail dot com> <CAAHN_R23vHH4B_=GUHFXAfcRL5gFrOp6dyBLcskCQNG5VswxAA at mail dot gmail dot com> <516B8C16 dot 1050802 at gmail dot com> <20130415101439 dot GA3110 at domone dot kolej dot mff dot cuni dot cz> <20130415111319 dot GB6152 at type dot bordeaux dot inria dot fr> <20130415121141 dot GA10611 at domone dot kolej dot mff dot cuni dot cz> <20130415121508 dot GF6152 at type dot bordeaux dot inria dot fr> <20130415123504 dot GA12790 at domone dot kolej dot mff dot cuni dot cz> <20130415124824 dot GW20323 at brightrain dot aerifal dot cx>
On Mon, Apr 15, 2013 at 08:48:24AM -0400, Rich Felker wrote:
> On Mon, Apr 15, 2013 at 02:35:04PM +0200, OndÅej BÃlka wrote:
> > > > > > A SIGBUS makes using vrange out of question. We simply cannot ignore user generated SIGBUS.
> > > > >
> > > > > Such SIGBUS would not happen unless the user accesses some freed memory,
> > > > > which he shouldn't be doing anyway.
> > > >
> > > > When kill -BUS pid became illegal?
> > >
> > > I don't understand how that relates to what we are talking about. I've
> > > never said sending -BUS was illegal. I've said that accessing freed
> > > memory is illegal.
> >
> > Accessing freed memory is illegal but not only way how that SIGBUS could
> > happen. It could be SIGBUS from kill which is perfectly legal.
>
> You misunderstand. glibc/malloc would not be _catching_ SIGBUS, so the
> fact that it's delivered when freed memory is accessed is irrelevant
> to applications unless they access freed memory (and then it's their
> fault they get it!). So I don't see what the problem is. This does not
> interfere with an application's use of SIGBUS whatsoever.
>
Sorry for noise, I misunderstand that we do not catch (which would be
problematic).
> Rich