Subject: Re: [PATCH] fdtable: Avoid triggering OOMs from alloc_fdmem

From: [email-masked] (Eric W. Biederman)
Date: Tue, 04 Feb 2014 10:53:35 -0800

Cong Wang <[email-masked]> writes:

> On Mon, Feb 3, 2014 at 9:26 PM, Eric W. Biederman <[email-masked]> wrote:
>> diff --git a/fs/file.c b/fs/file.c
>> index 771578b33fb6..db25c2bdfe46 100644
>> --- a/fs/file.c
>> +++ b/fs/file.c
>> @@ -34,7 +34,7 @@ static void *alloc_fdmem(size_t size)
>>          * vmalloc() if the allocation size will be considered "large" by the VM.
>>          */
>>         if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) {
>> -               void *data = kmalloc(size, GFP_KERNEL|__GFP_NOWARN);
>> +               void *data = kmalloc(size, GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY);
>>                 if (data != NULL)
>>                         return data;
>>         }
>
> Or try again without __GFP_NORETRY like we do in nelink mmap?

I think I would much rather keep the current semantics of return -ENOMEM
and keep the problem localized then trigger a box wide OOM thank you
very much.

Retrying the kmalloc without __GFP_NORETRY is pointless.  If you are in
the unlikely 0.01% of the time when the kmalloc fails it is almost
certainly going to fail again.  Writing out_of_memory() as kmalloc()
is pointless and very confusing.

The vmalloc won't fail unless you are on a 32bit box.  So it isn't a
case that anyone has to deal with in practice.

Eric

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