Re: [PATCH 6/6] libpager: Use libc heap for pagemap

[Sergey Bugaev]

On Thu, May 6, 2021 at 3:56 PM Sergey Bugaev <bugaevc@gmail.com> wrote:
> -      newaddr = mmap (0, newsize * sizeof (*p->pagemap),
> -                     PROT_READ|PROT_WRITE, MAP_ANON, 0, 0);
> +      void *newaddr = reallocarray (p->pagemap, off,
> +                                    sizeof (*p->pagemap));

It seems while fixing preexisting issues I accidentally introduces a
new one. Unlike mmap, reallocarray does not zero-initialize the newly
allocated memory; but other code expects new pagemap entries to be set
to zero. This is the cause of those tarfs hangs I've been seeing
lately.

I'm sorry, and here's a hotfix.

Sergey

-- >8 --
Subject: [PATCH] libpager: Properly zero-initialize pagemap

Unlike mmap () and calloc (), reallocarray () does not automatically
zero-fill the newly allocated memory. Do so explicitly.
---
 libpager/pagemap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libpager/pagemap.c b/libpager/pagemap.c
index 7bbb8c56..c7c86d60 100644
--- a/libpager/pagemap.c
+++ b/libpager/pagemap.c
@@ -32,6 +32,8 @@ _pager_pagemap_resize (struct pager *p, vm_address_t off)
       if (!newaddr)
         return errno;

+      memset ((short *) newaddr + p->pagemapsize, 0,
+              (off - p->pagemapsize) * sizeof (*p->pagemap));
       p->pagemap = newaddr;
       p->pagemapsize = off;
     }
-- 
2.31.1