cvs commit: src/sys/vm uma_core.c

[Brian Fundakowski Feldman]

On Sun, Jul 04, 2004 at 03:59:25PM +0000, Brian Feldman wrote:
> green       2004-07-04 15:59:25 UTC
> 
>   FreeBSD src repository
> 
>   Modified files:
>     sys/vm               uma_core.c 
>   Log:
>   Reextend the M_WAITOK-disabling-hack to all three of the mbuf-related
>   zones, and do it by direct comparison of uma_zone_t instead of strcmp.
>   
>   The mbuf subsystem used to provide M_TRYWAIT/M_DONTWAIT semantics, but
>   this is mostly no longer the case.  M_WAITOK has taken over the spot
>   M_TRYWAIT used to have, and for mbuf things, still may return NULL if
>   the code path is incorrectly holding a mutex going into mbuf allocation
>   functions.
>   
>   The M_WAITOK/M_NOWAIT semantics are absolute; though it may deadlock
>   the system to try to malloc or uma_zalloc something with a mutex held
>   and M_WAITOK specified, it is absolutely required to not return NULL
>   and will result in instability and/or security breaches otherwise.
>   There is still room to add the WITNESS_WARN() to all cases so that
>   we are notified of the possibility of deadlocks, but it cannot change
>   the value of the "badness" variable and allow allocation to actually
>   fail except for the specialized cases which used to be M_TRYWAIT.

Any subsequent desire to change the semantics of malloc(9) or
uma_zalloc(9) in the M_WAITOK case, such as this, absolutely must be
taken up with the Security Officer.

-- 
Brian Fundakowski Feldman                           \'[ FreeBSD ]''''''''''\
  <> green at FreeBSD.org                               \  The Power to Serve! \
 Opinions expressed are my own.                       \,,,,,,,,,,,,,,,,,,,,,,\