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.
long, not an int, and this causes "problems" on LP64be machines
(sparc64, etc). Assign the value to a temporary int and instrument
that instead. Should be fine until someone wants a message buffer
larger than two gigabytes.
This areas is called the comm pages. It is used to provide fast access to
several data and functions.
The comm pages are mapped starting at 0xffff800 (address chosed so that
absolute branch can be used, so it can be accessed even when dynamic linking
is not ready). NetBSD has the user stack here, so we need to provide a
Darwin-specific stack setup routine which sets the top of the stack at
0xbfff0000.
This implementation is not complete but it does enough to get MacOS X.3
starting again (static binaries run, dynamic binaries still have an issue).
in the comm pages functions, we only implement bcopy, pthread_self and
memcpy.
TODO:
- clean up the powerpc specific code from MD parts
- for now we map only one page to avoid a crash, we want two pages.
- write all the comm functions.
want more flexible namecache handling.
it just looks up a dnlc entry and vget() the result vnode.
ie. no automatic entry removal, no automatic vnode locking.
discussed on tech-kern@.
doesn't advance while we're waiting on the lock. In fact, try to take
the lock even before blocking interrupts: the lock is locking "lasttime"
against other callers of cc_microtime(), not against the clock routines,
and if we take a clock interrupt while waiting for the lock, that's one
we don't have to take after the computations, but before returning to
the caller, and that makes the data a little fresher to the caller.
Moreover, inverting the order of splXXX() and simple_lock() permits us
to unblock interrupts before doing the long division.
With this, finally, performance of "ntpd" on my MP i386 seems to be no
worse than on non-MP i386, so this may fix PR kern/24207.
for consistency with M_FREE() and m_freem(). Affected files:
sys/mbuf.h
kern/uipc_socket2.c
kern/uipc_mbuf.c
net/if_ethersubr.c
netatalk/ddp_input.c
nfs/nfs_socket.c
a ktraced file descriptor that has already been invalidated. Change
all ktrace functions to propagate the error from ktrwrite() and
check for it. Thanks to Pavel Cahyna for finding this and giving
a perfect bug report.
[should be pulled up for 2.0]
doing copy-on-write.
- Change VFS_SNAPSHOT() to return the snapshot vnode locked.
- Make the IO path for copy-on-write and snapshot-read more lightweight.
Avoids deadlocks where vn_rdwr(...READ...) has a shared lock and needs
to copy-on-write.
Avoids deadlocks/panics where to clean pages the copy-on-write needs
to allocate pages for its VOP_PUTPAGES().
L_COWINPROGRESS part approved by: Jason R. Thorpe <thorpej@netbsd.org>
overloading "usec". The counter isn't counting micro-seconds, and using
the same variable to mean two different things is false economy: with
this change, the compiled object is 72 bytes smaller on i386, and the
code is easier to understand, to boot.
We do an MGETHDR)() for each mbuf "packet" of the input chain, to hold
the socket address prepended to that "packet". If those MGETHDR()s
ever failed, we would leak all the successfully-allocated mbuf
headers. Leak noted by Yamamoto-san (yamt@NetBSD.org); thanks for catching it!
Add socketbuf invariant-checking macros to sbappendaddrchain(), and
replace a stray bcopy() with memcpy(), also as suggested by Yamamoto-san.
hannken