[PATCH] aio: Fix return code of io_submit() (RFC)

[Kent Overstreet <kmo@daterainc.com>]

io_submit() could return -EAGAIN on memory allocation failure when it should
really have been returning -ENOMEM. This could confuse applications (i.e. fio)
since -EAGAIN means "too many requests outstanding, wait until completions have
been reaped" and if the application actually was tracking outstanding
completions this wouldn't make a lot of sense.

NOTE:

the man page seems to imply that the current behaviour (-EAGAIN on allocation
failure) has always been the case. I don't think it makes a lot of sense, but
this should probably be discussed more widely in case applications have somehow
come to rely on the current behaviour...

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Zach Brown <zab@zabbo.net>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Slava Pestov <sp@daterainc.com>
---
 fs/aio.c | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 733750096b..556547044b 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -933,23 +933,14 @@ static inline struct kiocb *aio_get_req(struct kioctx *ctx)
 {
 	struct kiocb *req;
 
-	if (!get_reqs_available(ctx)) {
-		user_refill_reqs_available(ctx);
-		if (!get_reqs_available(ctx))
-			return NULL;
-	}
-
 	req = kmem_cache_alloc(kiocb_cachep, GFP_KERNEL|__GFP_ZERO);
 	if (unlikely(!req))
-		goto out_put;
+		return NULL;
 
 	percpu_ref_get(&ctx->reqs);
 
 	req->ki_ctx = ctx;
 	return req;
-out_put:
-	put_reqs_available(ctx, 1);
-	return NULL;
 }
 
 static void kiocb_free(struct kiocb *req)
@@ -1489,9 +1480,17 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
 		return -EINVAL;
 	}
 
+	if (!get_reqs_available(ctx)) {
+		user_refill_reqs_available(ctx);
+		if (!get_reqs_available(ctx))
+			return -EAGAIN;
+	}
+
 	req = aio_get_req(ctx);
-	if (unlikely(!req))
-		return -EAGAIN;
+	if (unlikely(!req)) {
+		ret = -ENOMEM;
+		goto out_put;
+	}
 
 	req->ki_filp = fget(iocb->aio_fildes);
 	if (unlikely(!req->ki_filp)) {
@@ -1533,9 +1532,10 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
 
 	return 0;
 out_put_req:
-	put_reqs_available(ctx, 1);
 	percpu_ref_put(&ctx->reqs);
 	kiocb_free(req);
+out_put:
+	put_reqs_available(ctx, 1);
 	return ret;
 }
 
-- 
2.1.1