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| -rw-r--r-- | share/man/man9/mutex.9 | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/share/man/man9/mutex.9 b/share/man/man9/mutex.9 index 3198b5f3be92..50bb085759fd 100644 --- a/share/man/man9/mutex.9 +++ b/share/man/man9/mutex.9 @@ -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 , |