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LinuxKPI: Do not wait for a grace period in rcu_barrier()

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Linux docs explicitly state that this is not required [1]:

"Important note: The rcu_barrier() function is not, repeat, not,
obligated to wait for a grace period.  It is instead only required to
wait for RCU callbacks that have already been posted.  Therefore, if
there are no RCU callbacks posted anywhere in the system, rcu_barrier()
is within its rights to return immediately.  Even if there are
callbacks posted, rcu_barrier() does not necessarily need to wait for
a grace period."

[1] https://www.kernel.org/doc/Documentation/RCU/Design/Requirements/Requirements.html

Reviewed by:	emaste, hselasky, manu
MFC after:	2 weeks
Differential revision:	https://reviews.freebsd.org/D30809
This commit is contained in:
Vladimir Kondratyev 2021-07-05 03:19:50 +03:00
parent c0862b2b1f
commit 1ab61a1932
1 changed files with 6 additions and 2 deletions
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8
sys/compat/linuxkpi/common/src/linux_rcu.c
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@ -367,8 +367,12 @@ linux_rcu_barrier(unsigned type)
MPASS(type < RCU_TYPE_MAX);
linux_synchronize_rcu(type);
/*
* This function is not obligated to wait for a grace period.
* It only waits for RCU callbacks that have already been posted.
* If there are no RCU callbacks posted, rcu_barrier() can return
* immediately.
*/
head = &linux_epoch_head[type];
/* wait for callbacks to complete */