Re: [Xen-devel] [RFC] KEXEC: allocate crash note buffers at boot time v3

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 01.12.11 at 14:59, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> On 01/12/11 12:56, Jan Beulich wrote:
>> Further, you shouldn't take a lock around a call to xmalloc() or alike
>> unless absolutely necessary. It is pretty simple to avoid here - you
>> really only need to lock around the storing of the pointer and maybe
>> the setup_note() calls (but be careful with returning -ENOMEM - you
>> shouldn't if the allocation fails, but you then find - under the lock -
>> that a pointer was already set by another CPU).
> 
> So what we should do is this:
> 
> xmalloc
> take lock
> check to see if the entry is been filled in the meantime.  if so, free
> the malloc'd region

Don't call xfree() with the lock held either, if possible.

> release lock
> only return -ENOMEM if we fail the malloc and the crash_note is still
> NULL when we take the lock

Jan


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