On 03/19/2015 03:27 PM, Jens Axboe wrote:
On 03/19/2015 03:00 PM, Tejun Heo wrote:
On Thu, Mar 19, 2015 at 04:58:33PM -0400, Jeff Moyer wrote:
Do you really want to do memory allocation in the exit path? That
sounds like a bad idea to me. (Of course, now you're going to point out
all the places that currently happens, right? ;-)
I think we just need a counter there - let everyone count down as they
exit and the last one trigger the completion, no?
Yeah that's a good point, that'd be cleaner too. I'll change it and test
that.
Here's a cleaner variant that pairs the completion even with an atomic
count. Works for me as well.
--
Jens Axboe
diff --git a/fs/aio.c b/fs/aio.c
index f8e52a1854c1..cabb5edd9bc1 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -77,6 +77,11 @@ struct kioctx_cpu {
unsigned reqs_available;
};
+struct ctx_rq_wait {
+ struct completion comp;
+ atomic_t count;
+};
+
struct kioctx {
struct percpu_ref users;
atomic_t dead;
@@ -115,7 +120,7 @@ struct kioctx {
/*
* signals when all in-flight requests are done
*/
- struct completion *requests_done;
+ struct ctx_rq_wait *rq_wait;
struct {
/*
@@ -535,8 +540,8 @@ static void free_ioctx_reqs(struct percpu_ref *ref)
struct kioctx *ctx = container_of(ref, struct kioctx, reqs);
/* At this point we know that there are no any in-flight requests */
- if (ctx->requests_done)
- complete(ctx->requests_done);
+ if (ctx->rq_wait && atomic_dec_and_test(&ctx->rq_wait->count))
+ complete(&ctx->rq_wait->comp);
INIT_WORK(&ctx->free_work, free_ioctx);
schedule_work(&ctx->free_work);
@@ -744,7 +749,7 @@ err:
* the rapid destruction of the kioctx.
*/
static int kill_ioctx(struct mm_struct *mm, struct kioctx *ctx,
- struct completion *requests_done)
+ struct ctx_rq_wait *wait)
{
struct kioctx_table *table;
@@ -773,7 +778,7 @@ static int kill_ioctx(struct mm_struct *mm, struct kioctx *ctx,
if (ctx->mmap_size)
vm_munmap(ctx->mmap_base, ctx->mmap_size);
- ctx->requests_done = requests_done;
+ ctx->rq_wait = wait;
percpu_ref_kill(&ctx->users);
return 0;
}
@@ -805,18 +810,24 @@ EXPORT_SYMBOL(wait_on_sync_kiocb);
void exit_aio(struct mm_struct *mm)
{
struct kioctx_table *table = rcu_dereference_raw(mm->ioctx_table);
- int i;
+ struct ctx_rq_wait wait;
+ int i, skipped;
if (!table)
return;
+ atomic_set(&wait.count, table->nr);
+ init_completion(&wait.comp);
+
+ skipped = 0;
for (i = 0; i < table->nr; ++i) {
struct kioctx *ctx = table->table[i];
- struct completion requests_done =
- COMPLETION_INITIALIZER_ONSTACK(requests_done);
- if (!ctx)
+ if (!ctx) {
+ skipped++;
continue;
+ }
+
/*
* We don't need to bother with munmap() here - exit_mmap(mm)
* is coming and it'll unmap everything. And we simply can't,
@@ -825,10 +836,12 @@ void exit_aio(struct mm_struct *mm)
* that it needs to unmap the area, just set it to 0.
*/
ctx->mmap_size = 0;
- kill_ioctx(mm, ctx, &requests_done);
+ kill_ioctx(mm, ctx, &wait);
+ }
+ if (!atomic_sub_and_test(skipped, &wait.count)) {
/* Wait until all IO for the context are done. */
- wait_for_completion(&requests_done);
+ wait_for_completion(&wait.comp);
}
RCU_INIT_POINTER(mm->ioctx_table, NULL);
@@ -1313,15 +1326,17 @@ SYSCALL_DEFINE1(io_destroy, aio_context_t, ctx)
{
struct kioctx *ioctx = lookup_ioctx(ctx);
if (likely(NULL != ioctx)) {
- struct completion requests_done =
- COMPLETION_INITIALIZER_ONSTACK(requests_done);
+ struct ctx_rq_wait wait;
int ret;
+ init_completion(&wait.comp);
+ atomic_set(&wait.count, 1);
+
/* Pass requests_done to kill_ioctx() where it can be set
* in a thread-safe way. If we try to set it here then we have
* a race condition if two io_destroy() called simultaneously.
*/
- ret = kill_ioctx(current->mm, ioctx, &requests_done);
+ ret = kill_ioctx(current->mm, ioctx, &wait);
percpu_ref_put(&ioctx->users);
/* Wait until all IO for the context are done. Otherwise kernel
@@ -1329,7 +1344,7 @@ SYSCALL_DEFINE1(io_destroy, aio_context_t, ctx)
* is destroyed.
*/
if (!ret)
- wait_for_completion(&requests_done);
+ wait_for_completion(&wait.comp);
return ret;
}
