Date: Tue, 17 Feb 2015 21:11:32 +0000 From: "hselasky (Hans Petter Selasky)" <phabric-noreply@FreeBSD.org> To: freebsd-net@freebsd.org Subject: [Differential] [Commented On] D1711: Changes to the callout code to restore active semantics and also add a test-framework and test to validate thecallout code (and potentially for use by other tests). Message-ID: <ee4a368c120008372d9a4fd3cf7ee132@localhost.localdomain> In-Reply-To: <differential-rev-PHID-DREV-vhk6ww63dvpj6egspuyt-req@FreeBSD.org> References: <differential-rev-PHID-DREV-vhk6ww63dvpj6egspuyt-req@FreeBSD.org>
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hselasky added a comment.
randall: You are right I confused the two c_cpu values.
Let my try to shoot again:
static struct callout_cpu *
callout_cpu_switch(struct callout *c, struct callout_cpu *cc, int new_cpu)
{
struct callout_cpu *new_cc;
MPASS(c != NULL && cc != NULL);
CC_LOCK_ASSERT(cc);
/*
* Avoid interrupts and preemption firing after the callout cpu
* is blocked in order to avoid deadlocks as the new thread
* may be willing to acquire the callout cpu lock.
*/
c->c_cpu = CPUBLOCK;
spinlock_enter();
CC_UNLOCK(cc);
new_cc = CC_CPU(new_cpu);
CC_LOCK(new_cc);
spinlock_exit();
c->c_cpu = new_cpu;
return (new_cc);
}
spinlock_enter() is not an SMP lock. It only protects the executing CPU from interrupts and task switching. Basically that means two threads can be stuck at:
new_cc = CC_CPU(new_cpu), meaning a single callout can be switched to multiple different CPU's at the same time? Or am I wrong?
--HPS
REVISION DETAIL
https://reviews.freebsd.org/D1711
To: rrs, gnn, rwatson, lstewart, jhb, kostikbel, sbruno, imp, adrian, hselasky
Cc: julian, hiren, jhb, kostikbel, emaste, delphij, neel, erj, freebsd-net
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