ref: 2733c957ef614631c1cb8b80f55a05cd0520dfc0
parent: 4acf15a832d6516f25e01b7a6301f51754405924
author: cinap_lenrek <cinap_lenrek@gmx.de>
date: Thu Jul 25 21:51:03 EDT 2013
ether82563: avoid deadlock due to icansleep() trying to acquire Rbpool.Lock icansleep() violates the lock ordering due to the following cases: rbfree(): ilock(Rbpool.Lock) -> wakeup(): spli(), lock(Rbpool.Rendez) sleep(): splhi(), lock(Rbpool.Rendez) -> icansleep(): ilock(Rbpool.Lock) erik fixed this moving the wakeup() out of the ilock() in rbfree(), but i think it is an error to try acquiering a ilock in sleeps wait condition function in general. so this is what we do: in the icansleep() function, we check for the *real* event we care about; that is, if theres a buffer available in the Rbpool. this is to handle the case when rbfree() makes a buffer available *before* it sees us setting p->starve = 1. p->starve is now just used to gate rbfree() from calling wakeup() as an optimization. this might cause spurious wakeups but they are not a problem. missed wakeups is the thing we have to prevent.
--- a/sys/src/9/pc/ether82563.c
+++ b/sys/src/9/pc/ether82563.c
@@ -792,14 +792,9 @@
icansleep(void *v)
{Rbpool *p;
- int r;
p = v;
- ilock(p);
- r = p->starve == 0;
- iunlock(p);
-
- return r;
+ return p->b != nil;
}
static Block*
@@ -1058,9 +1053,7 @@
print("i82563%d: no rx buffers\n", ctlr->pool);if(maysleep == 0)
return -1;
- ilock(p);
p->starve = 1;
- iunlock(p);
sleep(p, icansleep, p);
goto redux;
}
--
⑨