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Re: [PATCH 1/4] spapr: qemu_memalign() doesn't return NULL
From: |
Greg Kurz |
Subject: |
Re: [PATCH 1/4] spapr: qemu_memalign() doesn't return NULL |
Date: |
Tue, 27 Oct 2020 08:32:02 +0100 |
On Tue, 27 Oct 2020 12:56:40 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:
> On Mon, Oct 26, 2020 at 03:46:47PM +0100, Greg Kurz wrote:
> > On Mon, 26 Oct 2020 14:43:08 +0100
> > Philippe Mathieu-Daudé <philmd@redhat.com> wrote:
> >
> > > On 10/26/20 1:40 PM, Greg Kurz wrote:
> > > > qemu_memalign() aborts if OOM. Drop some dead code.
> > > >
> > > > Signed-off-by: Greg Kurz <groug@kaod.org>
> > > > ---
> > > > hw/ppc/spapr.c | 6 ------
> > > > hw/ppc/spapr_hcall.c | 8 ++------
> > > > 2 files changed, 2 insertions(+), 12 deletions(-)
> > > >
> > > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > > > index 0cc19b5863a4..f098d0ee6d98 100644
> > > > --- a/hw/ppc/spapr.c
> > > > +++ b/hw/ppc/spapr.c
> > > > @@ -1521,12 +1521,6 @@ void spapr_reallocate_hpt(SpaprMachineState
> > > > *spapr, int shift,
> > > > int i;
> > > >
> > > > spapr->htab = qemu_memalign(size, size);
> > > > - if (!spapr->htab) {
> > > > - error_setg_errno(errp, errno,
> > > > - "Could not allocate HPT of order %d",
> > > > shift);
> > > > - return;
> > >
> > > Wasn't the idea to use qemu_try_memalign() here?
> > >
> >
> > Well... I have mixed feeling around this. The HTAB was first
> > introduced by commit:
> >
> > commit f43e35255cffb6ac6230dd09d308f7909f823f96
> > Author: David Gibson <david@gibson.dropbear.id.au>
> > Date: Fri Apr 1 15:15:22 2011 +1100
> >
> > Virtual hash page table handling on pSeries machine
> >
> > using qemu_mallocz(), which was aborting on OOM. It then got
> > replaced by g_malloc0() when qemu_mallocz() got deprecated
> > and eventually by qemu_memalign() when KVM support was added.
> >
> > Surviving OOM when allocating the HTAB never seemed to be an
> > option until this commit that introduced the check:
> >
> > commit c5f54f3e31bf693f70a98d4d73ea5dbe05689857
> > Author: David Gibson <david@gibson.dropbear.id.au>
> > Date: Tue Feb 9 10:21:56 2016 +1000
> >
> > pseries: Move hash page table allocation to reset time
> >
> > I don't really see in the patch and in the changelog an obvious
> > desire to try to handle OOM.
>
>
> This one is probably ok. AFAICT all failures returned here would be
> more or less fatal in the caller, one way or another (&error_fatal in
> two cases, and failure to load an incoming migration stream in the
> other).
>
> > > > - }
> > > > -
> > > > memset(spapr->htab, 0, size);
> > > > spapr->htab_shift = shift;
> > > >
> > > > diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> > > > index 607740150fa2..34e146f628fb 100644
> > > > --- a/hw/ppc/spapr_hcall.c
> > > > +++ b/hw/ppc/spapr_hcall.c
> > > > @@ -361,12 +361,8 @@ static void *hpt_prepare_thread(void *opaque)
> > > > size_t size = 1ULL << pending->shift;
> > > >
> > > > pending->hpt = qemu_memalign(size, size);
> > > > - if (pending->hpt) {
> > > > - memset(pending->hpt, 0, size);
> > > > - pending->ret = H_SUCCESS;
> > > > - } else {
> > > > - pending->ret = H_NO_MEM;
> > >
> > > Ditto.
> > >
> >
> > This one was introduced by commit:
> >
> > commit 0b0b831016ae93bc14698a5d7202eb77feafea75
> > Author: David Gibson <david@gibson.dropbear.id.au>
> > Date: Fri May 12 15:46:49 2017 +1000
> >
> > pseries: Implement HPT resizing
> >
> > I agree that maybe the intent here could have been to use
> > qemu_try_memalign(),
> > but again I don't quite see any strong justification to handle OOM in the
> > changelog.
> >
> > David,
> >
> > Any insight to share ?
>
> Aborting on an HPT resize failure is definitely not ok, though. This
> one needs to be a qemu_try_memalign().
>
Ok, I'll fix that.
pgppymOrf5sr1.pgp
Description: OpenPGP digital signature
[PATCH 2/4] spapr: Use error_append_hint() in spapr_reallocate_hpt(), Greg Kurz, 2020/10/26
[PATCH 3/4] target/ppc: Fix kvmppc_load_htab_chunk() error reporting, Greg Kurz, 2020/10/26
[PATCH 4/4] spapr: Improve spapr_reallocate_hpt() error reporting, Greg Kurz, 2020/10/26
Re: [PATCH 4/4] spapr: Improve spapr_reallocate_hpt() error reporting, David Gibson, 2020/10/26