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Add some documentation of FreeBSD's special synchronization quirks

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which may surprise developers coming from Solaris, or other platforms
which have a similar interface, but slightly different rules.

Reviewed by: jhb, ru
This commit is contained in:
gallatin 2002-10-21 12:54:13 +00:00
parent e96a99374a
commit 1f58532c90
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share/man/man9/mutex.9
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@ -457,6 +457,26 @@ This option is used to quiet logging messages during individual mutex
operations.
This can be used to trim superfluous logging messages for debugging purposes.
.El
.Ss Giant
If Giant must be acquired, it must be acquired prior to acquiring
other mutexes.
Put another way: it is impossible to acquire Giant non-recursively while
holding another mutex.
It is possible to acquire other mutexes while holding Giant, and it is
possible to acquire Giant recursively while holding other mutexes.
.Ss Sleeping
Sleeping while holding a mutex (except for Giant) is almost never safe
and should be avoided.
There are numerous assertions which will fail if this is attempted.
.Ss Functions Which Access Memory in Userspace
No mutexes should be held (except for Giant) across functions which
access memory in userspace, such as
.Xr copyin 9 ,
.Xr copyout 9 ,
.Xr uiomove 9 ,
.Xr fuword 9 ,
etc.
No locks are needed when calling these functions.
.Sh SEE ALSO
.Xr condvar 9 ,
.Xr msleep 9 ,