Hey Peter,
Em 25/10/2024 06:03, Peter Zijlstra escreveu:
Extend the futex2 interface to be numa aware.
When FUTEX2_NUMA is specified for a futex, the user value is extended
to two words (of the same size). The first is the user value we all
know, the second one will be the node to place this futex on.
struct futex_numa_32 {
u32 val;
u32 node;
};
Maybe this should live at include/uapi/linux/futex.h.
When node is set to ~0, WAIT will set it to the current node_id such
that WAKE knows where to find it. If userspace corrupts the node value
between WAIT and WAKE, the futex will not be found and no wakeup will
happen.
When FUTEX2_NUMA is not set, the node is simply an extention of the
hash, such that traditional futexes are still interleaved over the
nodes.
This is done to avoid having to have a separate !numa hash-table.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Do you think some of those changes should be guarded with #ifdef
CONFIG_NUMA? Or is fine as it is? I see that most of NUMA_ values
defines to 1 anyway on !numa, but maybe the futex_init() and
futex_hash() would be a bit more simplified.
[...]
+static int futex_get_value(u32 *val, u32 __user *from, unsigned int flags)
+{
+ switch (futex_size(flags)) {
+ case 1: return __get_user(*val, (u8 __user *)from);
+ case 2: return __get_user(*val, (u16 __user *)from);
+ case 4: return __get_user(*val, (u32 __user *)from);
+ default: BUG();
+ }
+}
+
+static int futex_put_value(u32 val, u32 __user *to, unsigned int flags)
+{
+ switch (futex_size(flags)) {
+ case 1: return __put_user(val, (u8 __user *)to);
+ case 2: return __put_user(val, (u16 __user *)to);
+ case 4: return __put_user(val, (u32 __user *)to);
+ default: BUG();
+ }
+}
+
I found a bit confusing that this is here, shouldn't be at [PATCH 4/6]
futex: Enable FUTEX2_{8,16}?
