linux-kernel - [PATCH 1/8] pin iocb through aio.

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Message-Id: <20190310070822.11564-1-viro@ZenIV.linux.org.uk>
Date:   Sun, 10 Mar 2019 07:08:15 +0000
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        David Miller <davem@...emloft.net>,
        Jason Baron <jbaron@...mai.com>, kgraul@...ux.ibm.com,
        ktkhai@...tuozzo.com, kyeongdon.kim@....com,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>, pabeni@...hat.com,
        syzkaller-bugs@...glegroups.com, xiyou.wangcong@...il.com,
        Christoph Hellwig <hch@....de>,
        zhengbin <zhengbin13@...wei.com>, bcrl@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-aio@...ck.org,
        houtao1@...wei.com, yi.zhang@...wei.com
Subject: [PATCH 1/8] pin iocb through aio.

From: Linus Torvalds <torvalds@...ux-foundation.org>

aio_poll() is not the only case that needs file pinned; worse, while
aio_read()/aio_write() can live without pinning iocb itself, the
proof is rather brittle and can easily break on later changes.

Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 fs/aio.c | 37 +++++++++++++++++++++----------------
 1 file changed, 21 insertions(+), 16 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 3d9669d011b9..363d7d7c8bff 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1022,6 +1022,9 @@ static bool get_reqs_available(struct kioctx *ctx)
 /* aio_get_req
  *	Allocate a slot for an aio request.
  * Returns NULL if no requests are free.
+ *
+ * The refcount is initialized to 2 - one for the async op completion,
+ * one for the synchronous code that does this.
  */
 static inline struct aio_kiocb *aio_get_req(struct kioctx *ctx)
 {
@@ -1034,7 +1037,7 @@ static inline struct aio_kiocb *aio_get_req(struct kioctx *ctx)
 	percpu_ref_get(&ctx->reqs);
 	req->ki_ctx = ctx;
 	INIT_LIST_HEAD(&req->ki_list);
-	refcount_set(&req->ki_refcnt, 0);
+	refcount_set(&req->ki_refcnt, 2);
 	req->ki_eventfd = NULL;
 	return req;
 }
@@ -1067,15 +1070,18 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id)
 	return ret;
 }
 
+static inline void iocb_destroy(struct aio_kiocb *iocb)
+{
+	if (iocb->ki_filp)
+		fput(iocb->ki_filp);
+	percpu_ref_put(&iocb->ki_ctx->reqs);
+	kmem_cache_free(kiocb_cachep, iocb);
+}
+
 static inline void iocb_put(struct aio_kiocb *iocb)
 {
-	if (refcount_read(&iocb->ki_refcnt) == 0 ||
-	    refcount_dec_and_test(&iocb->ki_refcnt)) {
-		if (iocb->ki_filp)
-			fput(iocb->ki_filp);
-		percpu_ref_put(&iocb->ki_ctx->reqs);
-		kmem_cache_free(kiocb_cachep, iocb);
-	}
+	if (refcount_dec_and_test(&iocb->ki_refcnt))
+		iocb_destroy(iocb);
 }
 
 static void aio_fill_event(struct io_event *ev, struct aio_kiocb *iocb,
@@ -1749,9 +1755,6 @@ static ssize_t aio_poll(struct aio_kiocb *aiocb, const struct iocb *iocb)
 	INIT_LIST_HEAD(&req->wait.entry);
 	init_waitqueue_func_entry(&req->wait, aio_poll_wake);
 
-	/* one for removal from waitqueue, one for this function */
-	refcount_set(&aiocb->ki_refcnt, 2);
-
 	mask = vfs_poll(req->file, &apt.pt) & req->events;
 	if (unlikely(!req->head)) {
 		/* we did not manage to set up a waitqueue, done */
@@ -1782,7 +1785,6 @@ static ssize_t aio_poll(struct aio_kiocb *aiocb, const struct iocb *iocb)
 
 	if (mask)
 		aio_poll_complete(aiocb, mask);
-	iocb_put(aiocb);
 	return 0;
 }
 
@@ -1873,18 +1875,21 @@ static int __io_submit_one(struct kioctx *ctx, const struct iocb *iocb,
 		break;
 	}
 
+	/* Done with the synchronous reference */
+	iocb_put(req);
+
 	/*
 	 * If ret is 0, we'd either done aio_complete() ourselves or have
 	 * arranged for that to be done asynchronously.  Anything non-zero
 	 * means that we need to destroy req ourselves.
 	 */
-	if (ret)
-		goto out_put_req;
-	return 0;
+	if (!ret)
+		return 0;
+
 out_put_req:
 	if (req->ki_eventfd)
 		eventfd_ctx_put(req->ki_eventfd);
-	iocb_put(req);
+	iocb_destroy(req);
 out_put_reqs_available:
 	put_reqs_available(ctx, 1);
 	return ret;
-- 
2.11.0