Re: mlock() return value issue in kernel 2.6.23.17

On Thu, 31 Jul 2008 21:50:06 +0900
KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> wrote:


This testcase results with mlock failure with errno 14 that is EFAULT, but this
has been no where reported that mlock will give EFAULT, When i tested the same
on older kernel like 2.6.18, I got the correct result i.e errno 12 (ENOMEM).


I think in source code mlock(2), setting errno ENOMEM has been missed in
do_mlock() , on mlock_fixup() failure.

Let me know if my understanding is wrong!

Hi Halesh,

Could you try to following patch?

-----------------------------------------------------
SUSv3 require following behavior to mlock(2).

[ENOMEM]
Some or all of the address range specified by the addr and
len arguments does not correspond to valid mapped pages
in the address space of the process.

[EAGAIN]
Some or all of the memory identified by the operation could not
be locked when the call was made.


This rule isn't so nice and slighly strange.
but many people think POSIX/SUS compliance is important.


---
mm/memory.c | 16 +++++++++++++---
mm/mlock.c | 2 --
2 files changed, 13 insertions(+), 5 deletions(-)

Index: b/mm/memory.c
===================================================================
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2736,16 +2736,26 @@ int make_pages_present(unsigned long add

vma = find_vma(current->mm, addr);
if (!vma)
- return -1;
+ return -ENOMEM;
write = (vma->vm_flags & VM_WRITE) != 0;
BUG_ON(addr >= end);
BUG_ON(end > vma->vm_end);
len = DIV_ROUND_UP(end, PAGE_SIZE) - addr/PAGE_SIZE;
ret = get_user_pages(current, current->mm, addr,
len, write, 0, NULL, NULL);
- if (ret < 0)
+ if (ret < 0) {
+ /*
+ SUS require strange return value to mlock
+ - invalid addr generate to ENOMEM.
+ - out of memory should generate EAGAIN.
+ */
+ if (ret == -EFAULT)
+ ret = -ENOMEM;
+ else if (ret == -ENOMEM)
+ ret = -EAGAIN;
return ret;
- return ret == len ? 0 : -1;
+ }
+ return ret == len ? 0 : -ENOMEM;
}

#if !defined(__HAVE_ARCH_GATE_AREA)
Index: b/mm/mlock.c
===================================================================
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -78,8 +78,6 @@ success:

mm->locked_vm -= pages;
out:
- if (ret == -ENOMEM)
- ret = -EAGAIN;
return ret;
}



I assume that you tested it too?

If it comes down to a choice between complying with SuS versus
complying with earlier Linux versions then we'd usually prefer to
comply with earlier Linux versions.

I queued this, but would prefer to await confirmation that it has been
tested to take us back to the 2.6.18 interface, please.

Also, please send a Signed-off-by: for this change.
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