Attachment #95643 for bug #134074

View | Details | Raw Unified | Return to bug 134074
Collapse All | Expand All




When a thread waits on a condition, the mutex
is atomically released before the thread is blocked, then reacquired
before the function call returns.
.Ss Giant
Giant is a special instance of a sleep lock.
It has several special characteristics.
.Bl -enum
.It
It is recursive.
.It
Drivers can request that Giant be locked around them, but this is
going away.
.It
You can sleep while it has recursed, but other recursive locks cannot.
.It
Giant must be locked first before other locks.
.It
There are places in the kernel that drop Giant and pick it back up
again.
Sleep locks will do this before sleeping.
Parts of the Network or VM code may do this as well, depending on the
setting of a sysctl.
This means that you cannot count on Giant keeping other code from
running if your code sleeps, even if you want it to.
.El
.Ss Sleep/wakeup
The functions
.Fn tsleep ,

.Va Giant
mutex before the function returns.
.Pp
.Ss Giant
Giant is a special instance of a sleep lock.
It has several special characteristics.
.Bl -enum
.It
It is recursive.
.It
Drivers can request that Giant be locked around them, but this is
going away.
.It
You can sleep while it has recursed, but other recursive locks cannot.
.It
Giant must be locked first before other locks.
.It
There are places in the kernel that drop Giant and pick it back up
again.
Sleep locks will do this before sleeping.
Parts of the Network or VM code may do this as well, depending on the
setting of a sysctl.
This means that you cannot count on Giant keeping other code from
running if your code sleeps, even if you want it to.
.El
.Ss lockmanager locks
Largely deprecated.
See the

Lock order is important.
.Pp
.Em *2
Readers can recurse though writers can not.
Lock order is important.
.Pp
.Em *3
There are calls to atomically release this primitive when going to sleep
and reacquire it on wakeup (e.g.
.Fn mtx_sleep ,
.Fn rw_sleep

.Em *4
Though one can sleep holding an sx lock, one can also use
.Fn sx_sleep
which will atomically release this primitive when going to sleep and
reacquire it on wakeup.
.Ss Context mode table.
The next table shows what can be used in different contexts.

.Xr sleep 9 ,
.Xr sx 9 ,
.Xr LOCK_PROFILING 9 ,
.Xr witness 4
.Sh HISTORY
These
functions appeared in

Return to bug 134074

Lines 220-247 Link Here

(-)share/man/man9/locking.9 (-26 / +26 lines)
220	When a thread waits on a condition, the mutex	220	When a thread waits on a condition, the mutex
221	is atomically released before the thread is blocked, then reacquired	221	is atomically released before the thread is blocked, then reacquired
222	before the function call returns.	222	before the function call returns.
223	.Ss Giant
224	Giant is a special instance of a sleep lock.
225	It has several special characteristics.
226	.Bl -enum
227	.It
228	It is recursive.
229	.It
230	Drivers can request that Giant be locked around them, but this is
231	going away.
232	.It
233	You can sleep while it has recursed, but other recursive locks cannot.
234	.It
235	Giant must be locked first before other locks.
236	.It
237	There are places in the kernel that drop Giant and pick it back up
238	again.
239	Sleep locks will do this before sleeping.
240	Parts of the Network or VM code may do this as well, depending on the
241	setting of a sysctl.
242	This means that you cannot count on Giant keeping other code from
243	running if your code sleeps, even if you want it to.
244	.El
245	.Ss Sleep/wakeup	223	.Ss Sleep/wakeup
246	The functions	224	The functions
247	.Fn tsleep ,	225	.Fn tsleep ,
Lines 298-303 Link Here
298	.Va Giant	276	.Va Giant
299	mutex before the function returns.	277	mutex before the function returns.
300	.Pp	278	.Pp
		279	.Ss Giant
		280	Giant is a special instance of a sleep lock.
		281	It has several special characteristics.
		282	.Bl -enum
		283	.It
		284	It is recursive.
		285	.It
		286	Drivers can request that Giant be locked around them, but this is
		287	going away.
		288	.It
		289	You can sleep while it has recursed, but other recursive locks cannot.
		290	.It
		291	Giant must be locked first before other locks.
		292	.It
		293	There are places in the kernel that drop Giant and pick it back up
		294	again.
		295	Sleep locks will do this before sleeping.
		296	Parts of the Network or VM code may do this as well, depending on the
		297	setting of a sysctl.
		298	This means that you cannot count on Giant keeping other code from
		299	running if your code sleeps, even if you want it to.
		300	.El
301	.Ss lockmanager locks	301	.Ss lockmanager locks
302	Largely deprecated.	302	Largely deprecated.
303	See the	303	See the
Lines 325-335 Link Here
325	Lock order is important.	325	Lock order is important.
326	.Pp	326	.Pp
327	.Em *2	327	.Em *2
328	readers can recurse though writers can not.	328	Readers can recurse though writers can not.
329	Lock order is important.	329	Lock order is important.
330	.Pp	330	.Pp
331	.Em *3	331	.Em *3
332	There are calls atomically release this primitive when going to sleep	332	There are calls to atomically release this primitive when going to sleep
333	and reacquire it on wakeup (e.g.	333	and reacquire it on wakeup (e.g.
334	.Fn mtx_sleep ,	334	.Fn mtx_sleep ,
335	.Fn rw_sleep	335	.Fn rw_sleep
Lines 340-346 Link Here
340	.Em *4	340	.Em *4
341	Though one can sleep holding an sx lock, one can also use	341	Though one can sleep holding an sx lock, one can also use
342	.Fn sx_sleep	342	.Fn sx_sleep
343	which atomically release this primitive when going to sleep and	343	which will atomically release this primitive when going to sleep and
344	reacquire it on wakeup.	344	reacquire it on wakeup.
345	.Ss Context mode table.	345	.Ss Context mode table.
346	The next table shows what can be used in different contexts.	346	The next table shows what can be used in different contexts.
Lines 363-369 Link Here
363	.Xr sleep 9 ,	363	.Xr sleep 9 ,
364	.Xr sx 9 ,	364	.Xr sx 9 ,
365	.Xr LOCK_PROFILING 9 ,	365	.Xr LOCK_PROFILING 9 ,
366	.Xr WITNESS 9	366	.Xr witness 4
367	.Sh HISTORY	367	.Sh HISTORY
368	These	368	These
369	functions appeared in	369	functions appeared in