linux-kernel - __vm_enough_memory(), OVERCOMMIT_NEVER, current->mm, kernel thread

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Message-ID: <7123.1224602071@jrobl>
Date:	Wed, 22 Oct 2008 00:14:31 +0900
From:	hooanon05@...oo.co.jp
To:	linux-kernel@...r.kernel.org
Subject: __vm_enough_memory(), OVERCOMMIT_NEVER, current->mm, kernel thread

Hello all,

When sysctl_overcommit_memory is set OVERCOMMIT_NEVER,
__vm_enough_memory() refers current->mm.

For example,
# exportfs -i -o ... localhost:/tmpfs
# mkdir /tmp/w
# mount -o ... localhost:/tmpfs /tmp/w
# yes > /tmp/w/fileA

In this case, NFSD (kernel thread) calls shmem_file_write() or
shmem_write_begin() and __vm_enough_memory() is called. But current->mm
is NULL and the kernel crashes.
If a user have to set OVERCOMMIT_NEVER, where should we fix?

Junjiro R. Okajima
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