Messages in this thread | | | Date | Tue, 27 Mar 2007 06:07:57 -0500 | From | Jakub Jelinek <> | Subject | Re: [PATCH 2.6.21-rc4-mm1 4/4] sys_futex64 : allows 64bit futexes |
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On Wed, Mar 21, 2007 at 10:54:36AM +0100, Pierre.Peiffer@bull.net wrote: > This last patch is an adaptation of the sys_futex64 syscall provided in -rt > patch (originally written by Ingo Molnar). It allows the use of 64-bit futex. > > I have re-worked most of the code to avoid the duplication of the code. > > It does not provide the functionality for all architectures (only for x64 for now).
I don't think you should blindly add all operations to sys_futex64 without thinking what they really do. E.g. FUTEX_{{,UN,TRY}LOCK,CMP_REQUEUE}_PI doesn't really make any sense for 64-bit futexes, the format of PI futexes is hardcoded in the kernel and is always 32-bit, see FUTEX_TID_MASK, FUTEX_WAITERS, FUTEX_OWNER_DIED definitions. exit_robust_list/handle_futex_death will handle 32-bit PI futexes anyway. Similarly, sys_futex64 shouldn't support the obsolete operations that are there solely for compatibility (e.g. FUTEX_REQUEUE or FUTEX_FD).
When you just -ENOSYS on the PI ops, there is no need to implement futex_atomic_cmpxchg_inatomic64.
FUTEX_WAKE_OP is questionable for 64-bit, IMHO it is better to just -ENOSYS on it and only if anyone ever finds actual uses for it, add it.
For 64-bit futexes the only needed operations are actually FUTEX_WAIT and perhaps FUTEX_CMP_REQUEUE, so I wonder if it isn't better to just add FUTEX_WAIT64 and FUTEX_CMP_REQUEUE64 ops to sys_futex instead of adding a new syscall.
But the FUTEX_{{,UN,TRY}LOCK,CMP_REQUEUE}_PI removal for 64-bit futexes is IMHO the most important part of my complain.
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