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coroutine: use QEMU_DEFINE_STATIC_CO_TLS()

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Thread-Local Storage variables cannot be used directly from coroutine
code because the compiler may optimize TLS variable accesses across
qemu_coroutine_yield() calls. When the coroutine is re-entered from
another thread the TLS variables from the old thread must no longer be
used.

Use QEMU_DEFINE_STATIC_CO_TLS() for the current and leader variables.
The alloc_pool QSLIST needs a typedef so the return value of
get_ptr_alloc_pool() can be stored in a local variable.

One example of why this code is necessary: a coroutine that yields
before calling qemu_coroutine_create() to create another coroutine is
affected by the TLS issue.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20220307153853.602859-3-stefanha@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2022-03-07 15:38:52 +00:00 committed by Kevin Wolf
parent 34145a307d
commit ac387a08a9
1 changed files with 24 additions and 17 deletions
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41
util/qemu-coroutine.c
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@ -18,6 +18,7 @@
#include "qemu/atomic.h"
#include "qemu/coroutine.h"
#include "qemu/coroutine_int.h"
#include "qemu/coroutine-tls.h"
#include "block/aio.h"
/** Initial batch size is 64, and is increased on demand */
@ -29,17 +30,20 @@ enum {
static QSLIST_HEAD(, Coroutine) release_pool = QSLIST_HEAD_INITIALIZER(pool);
static unsigned int pool_batch_size = POOL_INITIAL_BATCH_SIZE;
static unsigned int release_pool_size;
static __thread QSLIST_HEAD(, Coroutine) alloc_pool = QSLIST_HEAD_INITIALIZER(pool);
static __thread unsigned int alloc_pool_size;
static __thread Notifier coroutine_pool_cleanup_notifier;
typedef QSLIST_HEAD(, Coroutine) CoroutineQSList;
QEMU_DEFINE_STATIC_CO_TLS(CoroutineQSList, alloc_pool);
QEMU_DEFINE_STATIC_CO_TLS(unsigned int, alloc_pool_size);
QEMU_DEFINE_STATIC_CO_TLS(Notifier, coroutine_pool_cleanup_notifier);
static void coroutine_pool_cleanup(Notifier *n, void *value)
{
Coroutine *co;
Coroutine *tmp;
CoroutineQSList *alloc_pool = get_ptr_alloc_pool();
QSLIST_FOREACH_SAFE(co, &alloc_pool, pool_next, tmp) {
QSLIST_REMOVE_HEAD(&alloc_pool, pool_next);
QSLIST_FOREACH_SAFE(co, alloc_pool, pool_next, tmp) {
QSLIST_REMOVE_HEAD(alloc_pool, pool_next);
qemu_coroutine_delete(co);
}
}
@ -49,27 +53,30 @@ Coroutine *qemu_coroutine_create(CoroutineEntry *entry, void *opaque)
Coroutine *co = NULL;
if (CONFIG_COROUTINE_POOL) {
co = QSLIST_FIRST(&alloc_pool);
CoroutineQSList *alloc_pool = get_ptr_alloc_pool();
co = QSLIST_FIRST(alloc_pool);
if (!co) {
if (release_pool_size > qatomic_read(&pool_batch_size)) {
/* Slow path; a good place to register the destructor, too. */
if (!coroutine_pool_cleanup_notifier.notify) {
coroutine_pool_cleanup_notifier.notify = coroutine_pool_cleanup;
qemu_thread_atexit_add(&coroutine_pool_cleanup_notifier);
Notifier *notifier = get_ptr_coroutine_pool_cleanup_notifier();
if (!notifier->notify) {
notifier->notify = coroutine_pool_cleanup;
qemu_thread_atexit_add(notifier);
}
/* This is not exact; there could be a little skew between
* release_pool_size and the actual size of release_pool. But
* it is just a heuristic, it does not need to be perfect.
*/
alloc_pool_size = qatomic_xchg(&release_pool_size, 0);
QSLIST_MOVE_ATOMIC(&alloc_pool, &release_pool);
co = QSLIST_FIRST(&alloc_pool);
set_alloc_pool_size(qatomic_xchg(&release_pool_size, 0));
QSLIST_MOVE_ATOMIC(alloc_pool, &release_pool);
co = QSLIST_FIRST(alloc_pool);
}
}
if (co) {
QSLIST_REMOVE_HEAD(&alloc_pool, pool_next);
alloc_pool_size--;
QSLIST_REMOVE_HEAD(alloc_pool, pool_next);
set_alloc_pool_size(get_alloc_pool_size() - 1);
}
}
@ -93,9 +100,9 @@ static void coroutine_delete(Coroutine *co)
qatomic_inc(&release_pool_size);
return;
}
if (alloc_pool_size < qatomic_read(&pool_batch_size)) {
QSLIST_INSERT_HEAD(&alloc_pool, co, pool_next);
alloc_pool_size++;
if (get_alloc_pool_size() < qatomic_read(&pool_batch_size)) {
QSLIST_INSERT_HEAD(get_ptr_alloc_pool(), co, pool_next);
set_alloc_pool_size(get_alloc_pool_size() + 1);
return;
}
}