From 56bc43f5d02bd0745d597db44c285bf78d083762 Mon Sep 17 00:00:00 2001 From: Konstantin Belousov Date: Fri, 15 May 2026 14:05:45 +0300 Subject: [PATCH] locking.9: warn about using sleepable lock address as a sleep channel Reviewed by: markj Sponsored by: The FreeBSD Foundation MFC after: 3 days Differential revision: https://reviews.freebsd.org/D57012 --- share/man/man9/locking.9 | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/share/man/man9/locking.9 b/share/man/man9/locking.9 index ad044b6e1d4..9afdcd56f4f 100644 --- a/share/man/man9/locking.9 +++ b/share/man/man9/locking.9 @@ -205,11 +205,6 @@ The functions and .Fn wakeup_one also handle event-based thread blocking. -Unlike condition variables, -arbitrary addresses may be used as wait channels and a dedicated -structure does not need to be allocated. -However, care must be taken to ensure that wait channel addresses are -unique to an event. If a thread must wait for an external event, it is put to sleep by .Fn tsleep , .Fn msleep , @@ -222,6 +217,16 @@ Threads may also wait using one of the locking primitive sleep routines or .Xr sx_sleep 9 . .Pp +Unlike condition variables, +arbitrary addresses may be used as wait channels and a dedicated +structure does not need to be allocated. +However, care must be taken to ensure that wait channel addresses are +unique to an event. +For example, the memory address of a sleepable lock such as a +.Xr sx 9 +must not be used as a sleep channel, because the lock implementation +will internally use the same address as a wait channel. +.Pp The parameter .Fa chan is an arbitrary address that uniquely identifies the event on which