[PATCH 3/7] aio: sanitize ki_list handling

[Christoph Hellwig]

Instead of handcoded non-null checks always initialize ki_list to an
empty list and use list_empty / list_empty_careful on it.  While we're
at it also error out on a double call to kiocb_set_cancel_fn instead
of ignoring it.

Signed-off-by: Christoph Hellwig <h...@lst.de>
Acked-by: Jeff Moyer <jmo...@redhat.com>
Reviewed-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Reviewed-by: Darrick J. Wong <darrick.w...@oracle.com>
---
 fs/aio.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 7c1855afd723..18507743757a 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -553,13 +553,12 @@ void kiocb_set_cancel_fn(struct kiocb *iocb, 
kiocb_cancel_fn *cancel)
        struct kioctx *ctx = req->ki_ctx;
        unsigned long flags;
 
-       spin_lock_irqsave(&ctx->ctx_lock, flags);
-
-       if (!req->ki_list.next)
-               list_add(&req->ki_list, &ctx->active_reqs);
+       if (WARN_ON_ONCE(!list_empty(&req->ki_list)))
+               return;
 
+       spin_lock_irqsave(&ctx->ctx_lock, flags);
+       list_add_tail(&req->ki_list, &ctx->active_reqs);
        req->ki_cancel = cancel;
-
        spin_unlock_irqrestore(&ctx->ctx_lock, flags);
 }
 EXPORT_SYMBOL(kiocb_set_cancel_fn);
@@ -1039,7 +1038,7 @@ static inline struct aio_kiocb *aio_get_req(struct kioctx 
*ctx)
                goto out_put;
 
        percpu_ref_get(&ctx->reqs);
-
+       INIT_LIST_HEAD(&req->ki_list);
        req->ki_ctx = ctx;
        return req;
 out_put:
@@ -1107,7 +1106,7 @@ static void aio_complete(struct kiocb *kiocb, long res, 
long res2)
                file_end_write(file);
        }
 
-       if (iocb->ki_list.next) {
+       if (!list_empty_careful(&iocb->ki_list)) {
                unsigned long flags;
 
                spin_lock_irqsave(&ctx->ctx_lock, flags);
-- 
2.17.0