- for structure fields that are conditionally present,
make those fields always present.
- for functions which are conditionally inline, make them never inline.
- remove some other functions which are conditionally defined but
don't actually do anything anymore.
- make a lock-debugging function conditional on only LOCKDEBUG.
as discussed on tech-kern some time back.
from Stephan Uphoff, FreeBSD PR/69964.
(http://www.freebsd.org/cgi/query-pr.cgi?pr=69964)
> The LK_WANT_EXCL and LK_WANT_UPGRADE bits act as mini-locks and can block
> other threads.
> Normally this is not a problem since the mini locks are upgraded to full loc
> and the release of the locks will unblock the other threads.
> However if a thread reset the bits without optaining a full lock
> other threads are not awoken.
> This can happens if obtaining the full lock fails because of a LK_SLEEPFAIL,
> or a signal (if lock priority includes PCATCH .. don't think this is used).
ensure that no one else have the same lock.
a patch from Stephan Uphoff, FreeBSD PR/69934.
(http://www.freebsd.org/cgi/query-pr.cgi?pr=69934)
> Upgrading a lock does not play well together with acquiring
> an exclusive lock and can lead to two threads being
> granted exclusive access.
>
> Problematic sequence:
> Thread A acquires a previous unlocked lock in shared mode.
> Thread B tries to acquire the same lock in exclusive mode
> and blocks.
> Thread A upgrades its lock - waking up thread B.
> Thread B wakes up and also acquires the same lock as it only checks
> if the lock is not shared or if someone wants to upgrade the lock
> and not if someone already upgraded the lock to an exclusive lock.
- Not enabled by default. Needs kernel option FFS_SNAPSHOT.
- Change parameters of ffs_blkfree.
- Let the copy-on-write functions return an error so spec_strategy
may fail if the copy-on-write fails.
- Change genfs_*lock*() to use vp->v_vnlock instead of &vp->v_lock.
- Add flag B_METAONLY to VOP_BALLOC to return indirect block buffer.
- Add a function ffs_checkfreefile needed for snapshot creation.
- Add special handling of snapshot files:
Snapshots may not be opened for writing and the attributes are read-only.
Use the mtime as the time this snapshot was taken.
Deny mtime updates for snapshot files.
- Add function transferlockers to transfer any waiting processes from
one lock to another.
- Add vfsop VFS_SNAPSHOT to take a snapshot and make it accessible through
a vnode.
- Add snapshot support to ls, fsck_ffs and dump.
Welcome to 2.0F.
Approved by: Jason R. Thorpe <thorpej@netbsd.org>
woken-up thread is guaranteed to pass the buck to the next guy before
going back to sleep, and the rest of the lockmgr() code doesn't do that.
from Bill Sommerfeld. fixes PR 14097.
SPINLOCK_SPIN_HOOK, so that we actually check for
pending IPIs on the Alpha more than once. Also,
when we call alpha_ipi_process(), make sure to go
to splipi().
are done inside of wakeup which is holding the sched lock. Printf can cause
wakeup to get called again (pty redirection of console message) which will
panic with sched lock already held.
This isn't a long term fix as not being able to printf vs. sched lock should
be cleaned up better but this avoids continual panics with lockdebug running
and an xterm -C.
to update it, so don't bother with <machine/atomic.h>
Flush kernel_lock_release_all() and kernel_lock_acquire_count() (which
didn't do spinlock accounting correctly), and replace them with
spinlock_release_all() and spinlock_acquire_count().
- In simple_lock_switchcheck(), allow/enforce exactly one lock to be
held: sched_lock.
- Per e-mail to tech-smp from Bill Sommerfeld, r/w spin locks have
an interlock at splsched(), rather than splhigh().
- LOCK_ASSERT(), which expands to KASSERT() if LOCKDEBUG.
- new simple_lock_held(), which tests if the calling CPU holds
the specified simple lock.
From Bill Sommerfeld, modified slightly by me.
simple locks are held by CPUs. Remove p_simple_locks (which was
unused anyway, really), and add a LOCKDEBUG check for held simple
locks in mi_switch(). Grow p_locks to an int to take up the space
previously used by p_simple_locks so that the proc structure doens't
change size.
- add a new global variable, doing_shutdown, which is nonzero if
vfs_shutdown() or panic() have been called.
- in panic, set RB_NOSYNC if doing_shutdown is already set on entry
so we don't reenter vfs_shutdown if we panic'ed there.
- in vfs_shutdown, don't use proc0's process for sys_sync unless
curproc is NULL.
- in lockmgr, attribute successful locks to proc0 if doing_shutdown
&& curproc==NULL, and panic if we can't get the lock right away; avoids the
spurious lockmgr DIAGNOSTIC panic from the ddb reboot command.
- in subr_pool, deal with curproc==NULL in the doing_shutdown case.
- in mfs_strategy, bitbucket writes if doing_shutdown, so we don't
wedge waiting for the mfs process.
- in ltsleep, treat ((curproc == NULL) && doing_shutdown) like the
panicstr case.
Appears to fix: kern/9239, kern/10187, kern/9367.
May also fix kern/10122.
contains the values __SIMPLELOCK_LOCKED and __SIMPLELOCK_UNLOCKED, which
replace the old SIMPLELOCK_LOCKED and SIMPLELOCK_UNLOCKED. These files
are also required to supply inline functions __cpu_simple_lock(),
__cpu_simple_lock_try(), and __cpu_simple_unlock() if locking is to be
supported on that platform (i.e. if MULTIPROCESSOR is defined in the
_KERNEL case). Change these functions to take an int * (&alp->lock_data)
rather than the struct simplelock * itself.
These changes make it possible for userland to use the locking primitives
by including <machine/lock.h>.
1) fix typo preventing compilation (missing comma).
2) in SLOCK_WHERE, display cpu number in the MP case.
3) the folowing race condition was observed in _simple_lock:
cpu 1 releases lock,
cpu 0 grabs lock
cpu 1 sees it's already locked.
cpu 1 sees that lock_holder== "cpu 1"
cpu 1 assumes that it already holds it and barfs.
cpu 0 sets lock_holder == "cpu 0"
Fix: set lock_holder to LK_NOCPU in _simple_unlock().
too. Remove some needless code duplication by adding a "drain" argument
to the ACQUIRE() macro (compiler can [and does] optimize the constant
conditional).
- Now compatible with MULTIPROCESSOR (requires other changes not yet
committed, but which will be later today).
- In addition to tracking simple locks, track exclusive spin locks.
- Count spin locks like we do sleep locks (in the cpu_info for this
CPU).
- Lock debug lists are now TAILQs, so as to make the locking order
more obvious when dumping the list.
Also, some suggestions from Bill Sommerfeld:
- SIMPLELOCK_LOCKED and SIMPLELOCK_UNLOCKED constants, which may be
defined in <machine/lock.h> (default to 1 and 0, respectively). This
makes it easier to support architectures which use test-and-clear
rather than test-and-set.
- Add __attribute__((__aligned__)) to the `lock_data' member of the
simplelock structure. This makes it easier to support architectures
which can only perform atomic operations on very-well-aligned memory
locations. NOTE: This changes the size of struct simplelock, and
will cause a version bump.
remove simplelockrecurse, lockpausetime and PAUSE():
none of these serve any purpose anymore.
in the LOCKDEBUG functions, expand the splhigh() region to
cover the entire function. without this there can still be races.
and system call now just return EFAULT). A complete fix will
presumably have to wait for UBC and/or for vnode locking protocols to
be revamped to allow use of shared locks.
could be done in one of 2 ways:
* call lk_init with LK_CANRECURSE, resulting in a lock that
always can be used recursively.
* call lockmgr with LK_CANRECURSE, meaning that it's ok if this
lock is already held by us.
Sometimes we need a locking type that says: take this lock now, exclusively,
but while I am holding it, I may go through a code path which could attempt
to get the lock again, and which is unaware that the lock might already
be taken. Implement LK_SETRECURSE for this purpose. Assume that locks and
unlocks come in matching pairs (they should), and check for this 'level'
using SETRECURSE locks.
erh