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epoch_block_wait: don't check TD_RUNNING

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struct epoch_thread is not type safe (stack allocated) and thus cannot be dereferenced from another CPU

Reported by: novel@
This commit is contained in:
Matt Macy 2018-08-09 05:18:27 +00:00
parent 456a4ad51e
commit 9fec45d8e5
1 changed files with 26 additions and 12 deletions
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38
sys/kern/subr_epoch.c
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@ -56,7 +56,7 @@ __FBSDID("$FreeBSD$");
static MALLOC_DEFINE(M_EPOCH, "epoch", "epoch based reclamation");
/* arbitrary --- needs benchmarking */
#define MAX_ADAPTIVE_SPIN 1000
#define MAX_ADAPTIVE_SPIN 100
#define MAX_EPOCHS 64
CTASSERT(sizeof(ck_epoch_entry_t) == sizeof(struct epoch_context));
@ -240,24 +240,38 @@ epoch_block_handler_preempt(struct ck_epoch *global __unused, ck_epoch_record_t
locksheld = td->td_locks;
spincount = 0;
counter_u64_add(block_count, 1);
/*
* We lost a race and there's no longer any threads
* on the CPU in an epoch section.
*/
if (TAILQ_EMPTY(&record->er_tdlist))
return;
if (record->er_cpuid != curcpu) {
/*
* If the head of the list is running, we can wait for it
* to remove itself from the list and thus save us the
* overhead of a migration
*/
if ((tdwait = TAILQ_FIRST(&record->er_tdlist)) != NULL &&
TD_IS_RUNNING(tdwait->et_td)) {
gen = record->er_gen;
thread_unlock(td);
do {
cpu_spinwait();
} while (tdwait == TAILQ_FIRST(&record->er_tdlist) &&
gen == record->er_gen && TD_IS_RUNNING(tdwait->et_td) &&
spincount++ < MAX_ADAPTIVE_SPIN);
thread_lock(td);
gen = record->er_gen;
thread_unlock(td);
/*
* We can't actually check if the waiting thread is running
* so we simply poll for it to exit before giving up and
* migrating.
*/
do {
cpu_spinwait();
} while (!TAILQ_EMPTY(&record->er_tdlist) &&
gen == record->er_gen &&
spincount++ < MAX_ADAPTIVE_SPIN);
thread_lock(td);
/*
* If the generation has changed we can poll again
* otherwise we need to migrate.
*/
if (gen != record->er_gen)
return;
}
/*
* Being on the same CPU as that of the record on which
* we need to wait allows us access to the thread