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Comments describing how to properly use the new lock_add functions

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and its respective companion.

Sponsored by:	Netflix Inc.
This commit is contained in:
Randall Stewart 2016-08-16 13:08:03 +00:00
parent b07fef500b
commit 0fa047b98c
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=304219
1 changed files with 19 additions and 0 deletions
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19
sys/netinet/tcp_timer.c
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@ -301,6 +301,25 @@ tcp_timer_delack(void *xtp)
CURVNET_RESTORE();
}
/*
* When a timer wants to remove a TCB it must
* hold the INP_INFO_RLOCK(). The timer function
* should only have grabbed the INP_WLOCK() when
* it entered. To safely switch to holding both the
* INP_INFO_RLOCK() and the INP_WLOCK() we must first
* grab a reference on the inp, this will hold the inp
* so that it can't be removed. We then unlock and grab
* the info-read lock. Once we have the INP_INFO_RLOCK() we
* proceed again to get the INP_WLOCK() but after that
* we must check if someone else deleted the pcb i.e.
* the inp_flags check. If so we return 1 otherwise
* we return 0.
*
* No matter which the tcp_inpinfo_lock_add() function
* returns the caller must afterwards call tcp_inpinfo_lock_del()
* to drop the locks and reference properly.
*/
int
tcp_inpinfo_lock_add(struct inpcb *inp)
{