The barriers prevent the instruction of setting/clearing the LP_BOUND flag
from reordering over where we want to prevent LWP migrations.
Note that the fix doesn't mean that there was a race condition. For now the API
is used only for psref and the combination use of them doesn't need the
barriers(*).
(*) https://mail-index.netbsd.org/tech-kern/2018/02/15/msg023101.html
Pointed out by Mateusz Guzik
curlwp_bind sets the LP_BOUND flag to l_pflags of the current LWP, which
prevents it from migrating to another CPU until curlwp_bindx is called.
Meanwhile, there are several ways that an LWP is migrated to another CPU and in
any cases the scheduler postpones a migration if a target LWP is running. One
example of LWP migrations is a load balancing; the scheduler periodically
explores CPU-hogging LWPs and schedule them to migrate (see sched_lwp_stats).
At that point the scheduler checks the LP_BOUND flag and if it's set to a LWP,
the scheduler doesn't schedule the LWP. A scheduled LWP is tried to be migrated
when it is leaving a running CPU, i.e., mi_switch. And mi_switch does NOT check
the LP_BOUND flag. So if an LWP is scheduled first and then it sets the
LP_BOUND flag, the LWP can be migrated regardless of the flag. To avoid this
race condition, we need to check the flag in mi_switch too.
For more details see https://mail-index.netbsd.org/tech-kern/2018/02/13/msg023079.html
_UC_MACHINE_FP() is a helper macro to extract from mcontext a frame pointer.
Don't rely on this interface as a compiler might strip frame pointer or
optimize it making this interface unreliable.
For hppa assume a small frame context, for larger frames FP might be located
in a different register (4 instead of 3).
For ia64 there is no strict frame pointer, and registers might rotate.
Reuse 79 following:
./gcc/config/ia64/ia64.h:#define HARD_FRAME_POINTER_REGNUM LOC_REG (79)
Once ia64 will mature, this should be revisited.
A macro can encapsulate a real function for extracting Frame Pointer on
more complex CPUs / ABIs.
For the remaining CPUs, reuse standard register as defined in appropriate ABI.
The direct users of this macro are LLVM and GCC with Sanitizers.
Proposed on tech-userlevel@.
Sponsored by <The NetBSD Foundation>
SADB_X_EXT_PZERO by default.
There doesn't seem to be a sanity check in the keysock API to make sure
this place is never reached, and it's better to fill in with zeros than
not filling in at all (and leaking uninitialized mbuf data).
If an IPv6 packet has large options, a necessary space for evacuation can
exceed the expected size (ah_pool_item_size). Give up using the pool_cache
if it happens.
Pointed out by maxv@
If an IPv6 packet has large options, a necessary space for evacuation can
exceed the expected size (ah_pool_item_size). Give up using the pool_cache
if it happens.
Pointed out by maxv@
We don't need to do so because we have a reference to it. And also
relooking-up one there may return an sp/sav that has different
parameters from an original one.
limit and the function returns true if a packet are still in the RX ring.
ixgbe_handle_que() didn't check the return value. Check the return vaule
and issue a softint.
This bug is derived from FreeBSD and ixv(4) has no this bug.
XXX pullup-8
