- Clean up the KTR tracepoints to be slighlty more consistent and useful
- Fix a bug in WITNESS where we would recurse indefinitely and blow the
stack when acquiring Giant after sleeping with a sleepable lock held.
Reported by: tanimura (3)
may need the clock lock for nanotime().
- Add KTR trace events for lock list manipulations and other witness
operations.
- Use a temporary variable instead of setting the lock list head directly
and then setting up the links to add a new lock list entry to the lock
list. This small race could result in witness "forgetting" about all
the locks held by this process temporarily during an interrupt.
- Close a more fatal race condition when removing a lock from a list.
Removing a lock from the list entails both decrementing the count of
items in this bucket as well as shuffling items in the current bucket up
a notch to replace the gap left by the removed item. Wrap these
operations in a critical section.
around, use a common function for looking up and extracting the tunables
from the kernel environment. This saves duplicating the same function
over and over again. This way typically has an overhead of 8 bytes + the
path string, versus about 26 bytes + the path string.
lock. Since we won't actually block on a try lock operation, it's not
a problem. Add a comment explaining why it is safe to skip lock order
checking with try locks.
- Remove the ithread list lock spin lock from the order list.
fail due to witness exhausting its internal resources and shutting down.
Reported by: Szilveszter Adam <sziszi@petra.hos.u-szeged.hu>
Tested by: David Wolfskill <david@catwhisker.org>
struct lock_instance that is stored in the per-process and per-CPU lock
lists. Previously, the lock lists just kept a pointer to each lock held.
That pointer is now replaced by a lock instance which contains a pointer
to the lock object, the file and line of the last acquisition of a lock,
and various flags about a lock including its recursion count.
- If we sleep while holding a sleepable lock, then mark that lock instance
as having slept and ignore any lock order violations that occur while
acquiring Giant when we wake up with slept locks. This is ok because of
Giant's special nature.
- Allow witness to differentiate between shared and exclusive locks and
unlocks of a lock. Witness will now detect the case when a lock is
acquired first in one mode and then in another. Mutexes are always
locked and unlocked exclusively. Witness will also now detect the case
where a process attempts to unlock a shared lock while holding an
exclusive lock and vice versa.
- Fix a bug in the lock list implementation where we used the wrong
constant to detect the case where a lock list entry was full.
can happen if witness runs out of resources during initialization or if
witness_skipspin is enabled.
Sleuthing by: Peter Jeremy <peter.jeremy@alcatel.com.au>
count drops to 0 in witness_destroy, set the w_name and w_file pointers
to point to the string "(dead)" and the w_line field to 0. This way,
if a mutex of a given name is used only in a module, then as long as
all mutexes in the module are destroyed when the module is unloaded,
witness will not maintain stale references to the mutex's name in the
module's data section causing a panic later on when the w_name or w_file
field's are examined.
list into a public witness_list_locks() function. Call this function
twice in witness_list() instead of using an evil goto.
- Adjust the 'show locks' command to take an optional parameter which
specifies the pid of a process to list the locks of. By default the
locks held by the current process are displayed.
locks were held, we could be preempted and switch CPU's in between the time
that we set a variable to the list of spin locks on our CPU and the time
that we checked that variable to ensure no spinlocks were held while
grabbing a sleep lock. Losing the race resulted in checking some other
CPU's spin lock list and bogusly panicing.
- Introduce lock classes and lock objects. Each lock class specifies a
name and set of flags (or properties) shared by all locks of a given
type. Currently there are three lock classes: spin mutexes, sleep
mutexes, and sx locks. A lock object specifies properties of an
additional lock along with a lock name and all of the extra stuff needed
to make witness work with a given lock. This abstract lock stuff is
defined in sys/lock.h. The lockmgr constants, types, and prototypes have
been moved to sys/lockmgr.h. For temporary backwards compatability,
sys/lock.h includes sys/lockmgr.h.
- Replace proc->p_spinlocks with a per-CPU list, PCPU(spinlocks), of spin
locks held. By making this per-cpu, we do not have to jump through
magic hoops to deal with sched_lock changing ownership during context
switches.
- Replace proc->p_heldmtx, formerly a list of held sleep mutexes, with
proc->p_sleeplocks, which is a list of held sleep locks including sleep
mutexes and sx locks.
- Add helper macros for logging lock events via the KTR_LOCK KTR logging
level so that the log messages are consistent.
- Add some new flags that can be passed to mtx_init():
- MTX_NOWITNESS - specifies that this lock should be ignored by witness.
This is used for the mutex that blocks a sx lock for example.
- MTX_QUIET - this is not new, but you can pass this to mtx_init() now
and no events will be logged for this lock, so that one doesn't have
to change all the individual mtx_lock/unlock() operations.
- All lock objects maintain an initialized flag. Use this flag to export
a mtx_initialized() macro that can be safely called from drivers. Also,
we on longer walk the all_mtx list if MUTEX_DEBUG is defined as witness
performs the corresponding checks using the initialized flag.
- The lock order reversal messages have been improved to output slightly
more accurate file and line numbers.
and change the u_int mtx_saveintr member of struct mtx to a critical_t
mtx_savecrit.
- On the alpha we no longer need a custom _get_spin_lock() macro to avoid
an extra PAL call, so remove it.
- Partially fix using mutexes with WITNESS in modules. Change all the
_mtx_{un,}lock_{spin,}_flags() macros to accept explicit file and line
parameters and rename them to use a prefix of two underscores. Inside
of kern_mutex.c, generate wrapper functions for
_mtx_{un,}lock_{spin,}_flags() (only using a prefix of one underscore)
that are called from modules. The macros mtx_{un,}lock_{spin,}_flags()
are mapped to the __mtx_* macros inside of the kernel to inline the
usual case of mutex operations and map to the internal _mtx_* functions
in the module case so that modules will use WITNESS and KTR logging if
the kernel is compiled with support for it.
if we hold a spin mutex, since we can trivially get into deadlocks if we
start switching out of processes that hold spinlocks. Checking to see if
interrupts were disabled was a sort of cheap way of doing this since most
of the time interrupts were only disabled when holding a spin lock. At
least on the i386. To fix this properly, use a per-process counter
p_spinlocks that counts the number of spin locks currently held, and
instead of checking to see if interrupts are disabled in the witness code,
check to see if we hold any spin locks. Since child processes always
start up with the sched lock magically held in fork_exit(), we initialize
p_spinlocks to 1 for child processes. Note that proc0 doesn't go through
fork_exit(), so it starts with no spin locks held.
Consulting from: cp
don't end up back at ourselves which would indicate deadlock.
- Add the proc lock to the witness dup_list as we may hold more than one
process lock at a time.
- Don't assert a mutex is owned in _mtx_unlock_sleep() as that is too late.
We do the checks in the macros instead.
update native priority, it is diffcult to get right and likely
to end up horribly wrong. Use an honestly wrong fixed value
that seems to work; PUSER for user threads, and the interrupt
priority for ithreads. Set it once when the process is created
and forget about it.
Suggested by: bde
Pointy hat: me
process's priority go through the roof when it released a (contested)
mutex. Only set the native priority in mtx_lock if hasn't already
been set.
Reviewed by: jhb
passed in filename and line number in the KTR tracepoint message.
- Even though it is #if 0'd code, change the code to detect that a process
is an interrupt thread to check p->p_ithd against NULL rather than
checking non-existant process flags from BSD/OS.
- Use '%p' to print pointers in KTR log messages instead of assuming
sizeof(int) == sizeof(void *).
- Don't set p_mtxname to NULL when releasing a mutex. It doesn't hurt
to leave it set (we don't clear w_mesg for example) and at least at
one time in the past, there used to be race conditions in the kernel
that would result in setting this to NULL causing the kernel to
dereference NULL.
- Make the _mtx_assert() function be compiled in if INVARIANTS_SUPPORT is
defined rather than if INVARIANTS is defined so that a KLD compiled
with INVARIANTS that uses mtx_assert() can be used with a kernel that
just has INVARIANT_SUPPORT compiled in.
- All processes go into the same array of queues, with different
scheduling classes using different portions of the array. This
allows user processes to have their priorities propogated up into
interrupt thread range if need be.
- I chose 64 run queues as an arbitrary number that is greater than
32. We used to have 4 separate arrays of 32 queues each, so this
may not be optimal. The new run queue code was written with this
in mind; changing the number of run queues only requires changing
constants in runq.h and adjusting the priority levels.
- The new run queue code takes the run queue as a parameter. This
is intended to be used to create per-cpu run queues. Implement
wrappers for compatibility with the old interface which pass in
the global run queue structure.
- Group the priority level, user priority, native priority (before
propogation) and the scheduling class into a struct priority.
- Change any hard coded priority levels that I found to use
symbolic constants (TTIPRI and TTOPRI).
- Remove the curpriority global variable and use that of curproc.
This was used to detect when a process' priority had lowered and
it should yield. We now effectively yield on every interrupt.
- Activate propogate_priority(). It should now have the desired
effect without needing to also propogate the scheduling class.
- Temporarily comment out the call to vm_page_zero_idle() in the
idle loop. It interfered with propogate_priority() because
the idle process needed to do a non-blocking acquire of Giant
and then other processes would try to propogate their priority
onto it. The idle process should not do anything except idle.
vm_page_zero_idle() will return in the form of an idle priority
kernel thread which is woken up at apprioriate times by the vm
system.
- Update struct kinfo_proc to the new priority interface. Deliberately
change its size by adjusting the spare fields. It remained the same
size, but the layout has changed, so userland processes that use it
would parse the data incorrectly. The size constraint should really
be changed to an arbitrary version number. Also add a debug.sizeof
sysctl node for struct kinfo_proc.
tracing in order to avoid duplication.
- Insert some tracepoints back into the mutex acq/rel code, thus ensuring
that we can trace all lock acq/rel's again.
- All CURPROC != NULL checks are MPASS()es (under MUTEX_DEBUG) because they
signify a serious mutex corruption.
- Change up some KASSERT()s to MPASS()es, and vice-versa, depending on the
type of problem we're debugging (INVARIANTS is used here to check that
the API is being used properly whereas MUTEX_DEBUG is used to ensure that
something general isn't happening that will have bad impact on mutex
locks).
Reminded by: jhb, jake, asmodai
will only display sleep mutexes held by the current process.
- Clean up some nits in the witness_display() function and add a ddb
command 'show witness' that dumps the hierarchy and order lists to the
console.
- Use queue(3) macros where appropriate.
- Resort the spin lock order list so that "com" is before "sched_lock".
Also, add appropriate #ifdef's around SMP and i386-specific mutexes.
- Add two new mutexes used to protect the ithread lists and tables to the
order list.
Requested by: bde (1)
mtx_enter(lock, type) becomes:
mtx_lock(lock) for sleep locks (MTX_DEF-initialized locks)
mtx_lock_spin(lock) for spin locks (MTX_SPIN-initialized)
similarily, for releasing a lock, we now have:
mtx_unlock(lock) for MTX_DEF and mtx_unlock_spin(lock) for MTX_SPIN.
We change the caller interface for the two different types of locks
because the semantics are entirely different for each case, and this
makes it explicitly clear and, at the same time, it rids us of the
extra `type' argument.
The enter->lock and exit->unlock change has been made with the idea
that we're "locking data" and not "entering locked code" in mind.
Further, remove all additional "flags" previously passed to the
lock acquire/release routines with the exception of two:
MTX_QUIET and MTX_NOSWITCH
The functionality of these flags is preserved and they can be passed
to the lock/unlock routines by calling the corresponding wrappers:
mtx_{lock, unlock}_flags(lock, flag(s)) and
mtx_{lock, unlock}_spin_flags(lock, flag(s)) for MTX_DEF and MTX_SPIN
locks, respectively.
Re-inline some lock acq/rel code; in the sleep lock case, we only
inline the _obtain_lock()s in order to ensure that the inlined code
fits into a cache line. In the spin lock case, we inline recursion and
actually only perform a function call if we need to spin. This change
has been made with the idea that we generally tend to avoid spin locks
and that also the spin locks that we do have and are heavily used
(i.e. sched_lock) do recurse, and therefore in an effort to reduce
function call overhead for some architectures (such as alpha), we
inline recursion for this case.
Create a new malloc type for the witness code and retire from using
the M_DEV type. The new type is called M_WITNESS and is only declared
if WITNESS is enabled.
Begin cleaning up some machdep/mutex.h code - specifically updated the
"optimized" inlined code in alpha/mutex.h and wrote MTX_LOCK_SPIN
and MTX_UNLOCK_SPIN asm macros for the i386/mutex.h as we presently
need those.
Finally, caught up to the interface changes in all sys code.
Contributors: jake, jhb, jasone (in no particular order)
mtx right now as it makes debugging harder. When we are in optimizing
mode, we can revisit this.
- Fix the KTR trace messages to use %p rather than 0x%p to avoid duplicate
0x's in KTR output.
- During witness_fixup, release Giant so that witness doesn't get confused.
Also, grab all_mtx while walking the list of mutexes.
- Remove w_sleep and w_recurse. Instead, perform checks on mutexes using
the mutex's mtx_flags field.
- Allow debug.witness_ddb and debug.witness_skipspin to be set from the
loader.
- Add Giant to the front of existing order_list entries to help ensure
Giant is always first.
- Add an order entry for the various proc locks. Note that this only
helps keep proc in order mostly as the allproc and proctree mutexes are
only obtained during a lockmgr operation on the specified mutex.
inline functions non-inlined. Hide parts of the mutex implementation that
should not be exposed.
Make sure that WITNESS code is not executed during boot until the mutexes
are fully initialized by SI_SUB_MUTEX (the original motivation for this
commit).
Submitted by: peter
