Re: [PATCH v2 2/2] mm/vmalloc: Print a warning message first on failure

Uladzislau Rezki
2021-05-10T10:56:42Z

On Sun, May 09, 2021 at 11:26:41PM +0200, Uladzislau Rezki wrote:
> On Sun, May 09, 2021 at 09:18:46PM +0100, Matthew Wilcox wrote:
> > On Sun, May 09, 2021 at 10:05:19PM +0200, Uladzislau Rezki wrote:
> > > On Sun, May 09, 2021 at 08:47:12PM +0100, Matthew Wilcox wrote:
> > > > > +++ b/mm/vmalloc.c
> > > > > @@ -2781,11 +2781,11 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
> > > > > }
> > > > >
> > > > > if (!area->pages) {
> > > > > - free_vm_area(area);
> > > > > warn_alloc(gfp_mask, NULL,
> > > > > "vmalloc size %lu allocation failure: "
> > > > > "page array size %lu allocation failed",
> > > > > nr_small_pages * PAGE_SIZE, array_size);
> > > > > + free_vm_area(area);
> > > > > return NULL;
> > > > > }
> > > >
> > > > I think this is a bad idea. We're clearly low on memory (a memory
> > > > allocation just failed). We should free the memory we have allocated
> > > > to improve the chances of the warning message making it out.
> > > Not sure if i fully follow you here. We do free the memory. The intention
> > > was to print a warning message first because, if, potentially, the
> > > free_vm_area(area) also does some prints it would be a bit messy from the
> > > point what has been broken first.
> > >
> > > So, could you please clarify what was your concern?
> >
> > We may need to allocate memory in order to emit the error message.
> >
> > Your commit message didn't mention the potential confusion, and I think
> > that is worth adding for a v4.
> I agree that the commit message should be updated in regard of potential
> confusion, because it was the main intention of this patch.
>
> I will upload a v4 tomorrow.
>
Please find the v4 version of the patch that is in question:

From 7e27e4ac8f299ae244e9e0e90e0292ae2c08d37d Mon Sep 17 00:00:00 2001
From: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
Date: Sat, 8 May 2021 23:41:21 +0200
Subject: [PATCH v4 1/1] mm/vmalloc: Print a warning message first on failure

When a memory allocation for array of pages are not succeed
emit a warning message as a first step and then perform the
further cleanup.

The reason it should be done in a right order is the clean
up function which is free_vm_area() can potentially also
follow its error paths what can lead to confusion what was
broken first.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
mm/vmalloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index dbc6744400d5..1f664a17d9ea 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2781,11 +2781,11 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
}

if (!area->pages) {
- free_vm_area(area);
warn_alloc(gfp_mask, NULL,
"vmalloc size %lu allocation failure: "
"page array size %lu allocation failed",
nr_small_pages * PAGE_SIZE, array_size);
+ free_vm_area(area);
return NULL;
}

--
2.20.1

--
Vlad Rezki