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SubjectRe: TMPFS over NFSv4
hope that the 2.6.27.48 or later will be shipped with SP1 :-)

__
tharindu.info

"those that can, do. Those that can’t, complain." -- Linus



On Tue, May 25, 2010 at 12:46 AM, Hugh Dickins <hughd@google.com> wrote:
> Hi Greg,
>
> On Mon, 24 May 2010, Alan Cox wrote:
>> On Mon, 24 May 2010 02:57:30 -0700
>> Hugh Dickins <hughd@google.com> wrote:
>> > On Mon, May 24, 2010 at 2:26 AM, Tharindu Rukshan Bamunuarachchi
>> > <btharindu@gmail.com> wrote:
>> > > thankx a lot Hugh ... I will try this out ... (bit harder patch
>> > > already patched SLES kernel :-p ) ....
>> >
>> > If patch conflicts are a problem, you really only need to put in the
>> > two-liner patch to mm/mmap.c: Alan was seeking perfection in
>> > the rest of the patch, but you can get away without it.
>> >
>> > >
>> > > BTW, what does Alan means by "strict overcommit" ?
>> >
>> > Ah, that phrase, yes, it's a nonsense, but many of us do say it by mistake.
>> > Alan meant to say "strict no-overcommit".
>>
>> No I always meant to say 'strict overcommit'. It avoids excess negatives
>> and "no noovercommit" discussions.
>>
>> I guess 'strict overcommit control' would have been clearer 8)
>>
>> Alan
>
> I see we've just missed 2.6.27.47-rc1, but if there's to be an -rc2,
> please include Alan's 2.6.28 oops fix below: which Tharindu appears
> to be needing - just now discussed on linux-mm and linux-nfs.
> Failing that, please queue it up for 2.6.27.48.
>
> Or if you'd prefer a smaller patch for -stable, then just the mm/mmap.c
> part of it should suffice: I think it's fair to say that the rest of the
> patch was more precautionary - as Alan describes, for catching other bugs,
> so good for an ongoing development tree, but not necessarily in -stable.
> (However, Alan may disagree - I've already misrepresented him once here!)
>
> Thanks,
> Hugh
>
> commit 731572d39fcd3498702eda4600db4c43d51e0b26
> Author: Alan Cox <alan@redhat.com>
> Date:   Wed Oct 29 14:01:20 2008 -0700
>
>    nfsd: fix vm overcommit crash
>
>    Junjiro R.  Okajima reported a problem where knfsd crashes if you are
>    using it to export shmemfs objects and run strict overcommit.  In this
>    situation the current->mm based modifier to the overcommit goes through a
>    NULL pointer.
>
>    We could simply check for NULL and skip the modifier but we've caught
>    other real bugs in the past from mm being NULL here - cases where we did
>    need a valid mm set up (eg the exec bug about a year ago).
>
>    To preserve the checks and get the logic we want shuffle the checking
>    around and add a new helper to the vm_ security wrappers
>
>    Also fix a current->mm reference in nommu that should use the passed mm
>
>    [akpm@linux-foundation.org: coding-style fixes]
>    [akpm@linux-foundation.org: fix build]
>    Reported-by: Junjiro R. Okajima <hooanon05@yahoo.co.jp>
>    Acked-by: James Morris <jmorris@namei.org>
>    Signed-off-by: Alan Cox <alan@redhat.com>
>    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
>    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
>
> diff --git a/include/linux/security.h b/include/linux/security.h
> index f5c4a51..c13f1ce 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -1585,6 +1585,7 @@ int security_syslog(int type);
>  int security_settime(struct timespec *ts, struct timezone *tz);
>  int security_vm_enough_memory(long pages);
>  int security_vm_enough_memory_mm(struct mm_struct *mm, long pages);
> +int security_vm_enough_memory_kern(long pages);
>  int security_bprm_alloc(struct linux_binprm *bprm);
>  void security_bprm_free(struct linux_binprm *bprm);
>  void security_bprm_apply_creds(struct linux_binprm *bprm, int unsafe);
> @@ -1820,6 +1821,11 @@ static inline int security_vm_enough_memory(long pages)
>        return cap_vm_enough_memory(current->mm, pages);
>  }
>
> +static inline int security_vm_enough_memory_kern(long pages)
> +{
> +       return cap_vm_enough_memory(current->mm, pages);
> +}
> +
>  static inline int security_vm_enough_memory_mm(struct mm_struct *mm, long pages)
>  {
>        return cap_vm_enough_memory(mm, pages);
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 74f4d15..de14ac2 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -175,7 +175,8 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
>
>        /* Don't let a single process grow too big:
>           leave 3% of the size of this process for other processes */
> -       allowed -= mm->total_vm / 32;
> +       if (mm)
> +               allowed -= mm->total_vm / 32;
>
>        /*
>         * cast `allowed' as a signed long because vm_committed_space
> diff --git a/mm/nommu.c b/mm/nommu.c
> index 2696b24..7695dc8 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -1454,7 +1454,8 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
>
>        /* Don't let a single process grow too big:
>           leave 3% of the size of this process for other processes */
> -       allowed -= current->mm->total_vm / 32;
> +       if (mm)
> +               allowed -= mm->total_vm / 32;
>
>        /*
>         * cast `allowed' as a signed long because vm_committed_space
> diff --git a/mm/shmem.c b/mm/shmem.c
> index d38d7e6..0ed0752 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -161,8 +161,8 @@ static inline struct shmem_sb_info *SHMEM_SB(struct super_block *sb)
>  */
>  static inline int shmem_acct_size(unsigned long flags, loff_t size)
>  {
> -       return (flags & VM_ACCOUNT)?
> -               security_vm_enough_memory(VM_ACCT(size)): 0;
> +       return (flags & VM_ACCOUNT) ?
> +               security_vm_enough_memory_kern(VM_ACCT(size)) : 0;
>  }
>
>  static inline void shmem_unacct_size(unsigned long flags, loff_t size)
> @@ -179,8 +179,8 @@ static inline void shmem_unacct_size(unsigned long flags, loff_t size)
>  */
>  static inline int shmem_acct_block(unsigned long flags)
>  {
> -       return (flags & VM_ACCOUNT)?
> -               0: security_vm_enough_memory(VM_ACCT(PAGE_CACHE_SIZE));
> +       return (flags & VM_ACCOUNT) ?
> +               0 : security_vm_enough_memory_kern(VM_ACCT(PAGE_CACHE_SIZE));
>  }
>
>  static inline void shmem_unacct_blocks(unsigned long flags, long pages)
> diff --git a/security/security.c b/security/security.c
> index 255b085..c0acfa7 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -198,14 +198,23 @@ int security_settime(struct timespec *ts, struct timezone *tz)
>
>  int security_vm_enough_memory(long pages)
>  {
> +       WARN_ON(current->mm == NULL);
>        return security_ops->vm_enough_memory(current->mm, pages);
>  }
>
>  int security_vm_enough_memory_mm(struct mm_struct *mm, long pages)
>  {
> +       WARN_ON(mm == NULL);
>        return security_ops->vm_enough_memory(mm, pages);
>  }
>
> +int security_vm_enough_memory_kern(long pages)
> +{
> +       /* If current->mm is a kernel thread then we will pass NULL,
> +          for this specific case that is fine */
> +       return security_ops->vm_enough_memory(current->mm, pages);
> +}
> +
>  int security_bprm_alloc(struct linux_binprm *bprm)
>  {
>        return security_ops->bprm_alloc_security(bprm);
>
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