linux-kernel - Re: [RFC PATCH v2 1/4] mm/vmalloc: warn on invalid vmalloc gfp flags

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Message-ID: <aQzHed0RfWBs3lK1@milan>
Date: Thu, 6 Nov 2025 17:06:17 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
Cc: Uladzislau Rezki <urezki@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [RFC PATCH v2 1/4] mm/vmalloc: warn on invalid vmalloc gfp flags

On Wed, Nov 05, 2025 at 04:00:19PM -0800, Vishal Moola (Oracle) wrote:
> On Wed, Nov 05, 2025 at 02:16:24PM +0100, Uladzislau Rezki wrote:
> > > On Mon, Nov 03, 2025 at 11:04:26AM -0800, Vishal Moola (Oracle) wrote:
> > > > Vmalloc explicitly supports a list of flags, but we never enforce them.
> > > > vmalloc has been trying to handle unsupported flags by clearing and
> > > > setting flags wherever necessary. This is messy and makes the code
> > > > harder to understand, when we could simply check for a supported input
> > > > immediately instead.
> > > >
> > > > Define a helper mask and function telling callers they have passed in
> > > > invalid flags, and clear those unsupported vmalloc flags.
> > > >
> > > > Suggested-by: Christoph Hellwig <hch@...radead.org>
> > > > Signed-off-by: Vishal Moola (Oracle) <vishal.moola@...il.com>
> > > > ---
> > > >  mm/vmalloc.c | 24 ++++++++++++++++++++++++
> > > >  1 file changed, 24 insertions(+)
> > > >
> > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > > index 0832f944544c..290016c7fb58 100644
> > > > --- a/mm/vmalloc.c
> > > > +++ b/mm/vmalloc.c
> > > > @@ -3911,6 +3911,26 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
> > > >       return NULL;
> > > >  }
> > > >
> > > > +/*
> > > > + * See __vmalloc_node_range() for a clear list of supported vmalloc flags.
> > > > + * This gfp lists all flags currently passed through vmalloc. Currently,
> > > > + * __GFP_ZERO is used by BFP and __GFP_NORETRY is used by percpu.
> > > > + */
> > > > +#define GFP_VMALLOC_SUPPORTED (GFP_KERNEL | GFP_ATOMIC | GFP_NOWAIT |\
> > > > +                             __GFP_NOFAIL |  __GFP_ZERO | __GFP_NORETRY)
> > > > +
> > Also we do support %GFP_NOFS and %GFP_NOIO flags.
> 
> Both of those are subsets of GFP_KERNEL, so I felt it was redundant to
> add.
>
Yep, that is true. But then you need to explicitly check which bits
GFP_KERNEL includes. I mean the white-list mask becomes less informative
for people who check or review the vmalloc code.

But you decide, i do not have a strong opinion.

--
Uladzislau Rezki