usbnet_detach (or its caller) stops all users before it returns.
If un->un_pri is null at this point, there's a bug -- something
didn't wait for everything to finish before calling usbnet_detach.
The unit-tests for meta mode do not depend on filemon.
Adding nofilemon to .MAKE.MODE allows these to pass on
a system that would use filemon_dev but does not have
the module loaded.
With the page cache, writing data to a file may demand to read contents
from a storage to fill a page in the page cache first.
Opening a file with write-only mode by a user lets a mount_9p process
open a file with write-only mode too at a 9p server. Thus, a read
request to the file from the page cache fails.
So we need to open a file always with read mode (internally) even if it
is opened with write-only mode by a user.
Note that the change doesn't mean that mount_9p allows users to read
contents from a file that is opened with write-only mode.
Something seems to be wrong with it, causing the display to get
stuck. To be diagnosed -- this is a performance optimization, but
it's better to work than to fail to work even if failing to work
costs a little less energy!
The Intel i915 graphics driver needs to receive ACPI VGA 0x80
notifications, but with NetBSD's ACPI API, each ACPI node -- such as
the VGA node -- can only have one notifier attached, and acpivga(4)
already uses it.
Previously, the string literals "1" "2" "3" "4" were concatenated in the
order "23", "234", "1234". This influenced the location of the
diagnostics for traditional C (which doesn't know concatenation at all)
and for mixing regular strings and wide strings.
Now the diagnostics occur exactly where they are expected. The first
string literal defines whether the whole string is regular or wide, and
any further string literals must match it.
In traditional C mode, there are more diagnostics than before, but that
doesn't hurt since they are still correct and nobody uses lint in
traditional C mode anyway.
Same as mutex_exit. Relevant only on cnMIPS where the store buffers
get clogged. Recommended by the Cavium documentation. No semantic
change, only performance -- this only adds a barrier in some cases
where there was none before, so it can't hurt correctness.
This change deletes memory barriers on non-Octeon MP. However, all
the appropriate acquire and release barriers are already used in
mutex stubs, and no barriers are needed in atomic_* unless we set
__HAVE_ATOMIC_AS_MEMBAR which we don't on MIPS. So this should be
safe.
Unclear whether we need this even on Octeon -- don't have a clear
reference on why it's here.
BDSYNC is used for membar_sync, which is supposed to be a full
sequential consistency barrier, which is not provided by syncw, so
this is necessary for correctness.
BDSYNC is not used for anything else, so this can't hurt performance,
except where it was necessary for correctness anyway or where the
semantic choice of membar_sync was too strong anyway.
This change deletes a memory barrier. However, it should be safe:
The semantic requirement for this is already provided by the SYNC_REL
above, before the ll. And as currently defined, SYNC_REL is at least
as strong as SYNC, so this change can't hurt correctness on its own
(barring CPU errata, which would apply to other users of SYNC_REL and
can be addressed in the definition of SYNC_REL).
Later, perhaps we can relax SYNC_REL to syncw on Octeon if we prove
that it is correct (e.g., if Octeon follows the SPARCv9 partial store
order semantics).
Nix now-unused SYNC macro in asm.h.
This change should be safe because it doesn't remove or weaken any
memory barriers, but does add, clarify, or strengthen barriers.
Goals:
- Make sure mutex_enter/exit and mutex_spin_enter/exit have
acquire/release semantics.
- New macros make maintenance easier and purpose clearer:
. SYNC_ACQ is for load-before-load/store barrier, and BDSYNC_ACQ
for a branch delay slot -- currently defined as plain sync for MP
and nothing, or nop, for UP; thus it is no weaker than SYNC and
BDSYNC as currently defined, which is syncw on Octeon, plain sync
on non-Octeon MP, and nothing/nop on UP.
It is not clear to me whether load-then-syncw or ll/sc-then-syncw
or even bare load provides load-acquire semantics on Octeon -- if
no, this will fix bugs; if yes (like it is on SPARC PSO), we can
relax SYNC_ACQ to be syncw or nothing later.
. SYNC_REL is for load/store-before-store barrier -- currently
defined as plain sync for MP and nothing for UP.
It is not clear to me whether syncw-then-store is enough for
store-release on Octeon -- if no, we can leave this as is; if
yes, we can relax SYNC_REL to be syncw on Octeon.
. SYNC_PLUNGER is there to flush clogged Cavium store buffers, and
BDSYNC_PLUNGER for a branch delay slot -- syncw on Octeon,
nothing or nop on non-Octeon.
=> This is not necessary (or, as far as I'm aware, sufficient)
for acquire semantics -- it serves only to flush store buffers
where stores might otherwise linger for hundreds of thousands
of cycles, which would, e.g., cause spin locks to be held for
unreasonably long durations.
Newerish revisions of the MIPS ISA also have finer-grained sync
variants that could be plopped in here.
Mechanism:
Insert these barriers in the right places, replacing only those where
the definition is currently equivalent, so this change is safe.
- Replace #ifdef _MIPS_ARCH_OCTEONP / syncw / #endif at the end of
atomic_cas_* by SYNC_PLUNGER, which is `sync 4' (a.k.a. syncw) if
__OCTEON__ and empty otherwise.
=> From what I can tell, __OCTEON__ is defined in at least as many
contexts as _MIPS_ARCH_OCTEONP -- i.e., there are some Octeons
with no _MIPS_ARCH_OCTEONP, but I don't know if any of them are
relevant to us or ever saw the light of day outside Cavium; we
seem to buid with `-march=octeonp' so this is unlikely to make a
difference. If it turns out that we do care, well, now there's
a central place to make the distinction for sync instructions.
- Replace post-ll/sc SYNC by SYNC_ACQ in _atomic_cas_*, which are
internal kernel versions used in sys/arch/mips/include/lock.h where
it assumes they have load-acquire semantics. Should move this to
lock.h later, since we _don't_ define __HAVE_ATOMIC_AS_MEMBAR on
MIPS and so the extra barrier might be costly.
- Insert SYNC_REL before ll/sc, and replace post-ll/sc SYNC by
SYNC_ACQ, in _ucas_*, which is used without any barriers in futex
code and doesn't mention barriers in the man page so I have to
assume it is required to be a release/acquire barrier.
- Change BDSYNC to BDSYNC_ACQ in mutex_enter and mutex_spin_enter.
This is necessary to provide load-acquire semantics -- unclear if
it was provided already by syncw on Octeon, but it seems more
likely that either (a) no sync or syncw is needed at all, or (b)
syncw is not enough and sync is needed, since syncw is only a
store-before-store ordering barrier.
- Insert SYNC_REL before ll/sc in mutex_exit and mutex_spin_exit.
This is currently redundant with the SYNC already there, but
SYNC_REL more clearly identifies the necessary semantics in case we
want to define it differently on different systems, and having a
sync in the middle of an ll/sc is a bit weird and possibly not a
good idea, so I intend to (carefully) remove the redundant SYNC in
a later change.
- Change BDSYNC to BDSYNC_PLUNGER at the end of mutex_exit. This has
no semantic change right now -- it's syncw on Octeon, sync on
non-Octeon MP, nop on UP -- but we can relax it later to nop on
non-Cavium MP.
- Leave LLSCSYNC in for now -- it is apparently there for a Cavium
erratum, but I'm not sure what the erratum is, exactly, and I have
no reference for it. I suspect these can be safely removed, but we
might have to double up some other syncw instructions -- Linux uses
it only in store-release sequences, not at the head of every ll/sc.
There is no need to make this variable externally visible. There are
several more variables in this file that could be unexported, leave
these for someone who knows whether vmstat.c is used by other parts of
the tree as well.
No functional change, OK mrg.
This only applies to traditional C and ensures that the behavior is
preserved when rearranging the C parser to evaluate string concatenation
from left to right.
No functional change. As before, the string literals "1" "2" "3" are
not concatenated from left to right, instead concatenation starts with
"23" and then proceeds to "123".
riastradh