Gitweb:     http://git.kernel.org/linus/87c3a86e1c220121d0ced59d1a71e78ed9abc6dd
Commit:     87c3a86e1c220121d0ced59d1a71e78ed9abc6dd
Parent:     d0115552cdb0b4d4146975889fee2e9355515c4b
Author:     Davide Libenzi <davidel@xmailserver.org>
AuthorDate: Wed Mar 18 17:04:19 2009 -0700
Committer:  Linus Torvalds <torvalds@linux-foundation.org>
CommitDate: Thu Mar 19 15:57:18 2009 -0700

    eventfd: remove fput() call from possible IRQ context
    
    Remove a source of fput() call from inside IRQ context.  Myself, like Eric,
    wasn't able to reproduce an fput() call from IRQ context, but Jeff said he was
    able to, with the attached test program.  Independently from this, the bug is
    conceptually there, so we might be better off fixing it.  This patch adds an
    optimization similar to the one we already do on ->ki_filp, on ->ki_eventfd.
    Playing with ->f_count directly is not pretty in general, but the alternative
    here would be to add a brand new delayed fput() infrastructure, that I'm not
    sure is worth it.
    
    Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
    Cc: Benjamin LaHaise <bcrl@kvack.org>
    Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
    Cc: Eric Dumazet <dada1@cosmosbay.com>
    Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
    Cc: Zach Brown <zach.brown@oracle.com>
    Cc: <stable@kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 fs/aio.c |   37 +++++++++++++++++++++++++++----------
 1 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 8fa77e2..4a9d4d6 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -443,7 +443,7 @@ static struct kiocb *__aio_get_req(struct kioctx *ctx)
 	req->private = NULL;
 	req->ki_iovec = NULL;
 	INIT_LIST_HEAD(&req->ki_run_list);
-	req->ki_eventfd = ERR_PTR(-EINVAL);
+	req->ki_eventfd = NULL;
 
 	/* Check if the completion queue has enough free space to
 	 * accept an event from this io.
@@ -485,8 +485,6 @@ static inline void really_put_req(struct kioctx *ctx, struct kiocb *req)
 {
 	assert_spin_locked(&ctx->ctx_lock);
 
-	if (!IS_ERR(req->ki_eventfd))
-		fput(req->ki_eventfd);
 	if (req->ki_dtor)
 		req->ki_dtor(req);
 	if (req->ki_iovec != &req->ki_inline_vec)
@@ -508,8 +506,11 @@ static void aio_fput_routine(struct work_struct *data)
 		list_del(&req->ki_list);
 		spin_unlock_irq(&fput_lock);
 
-		/* Complete the fput */
-		__fput(req->ki_filp);
+		/* Complete the fput(s) */
+		if (req->ki_filp != NULL)
+			__fput(req->ki_filp);
+		if (req->ki_eventfd != NULL)
+			__fput(req->ki_eventfd);
 
 		/* Link the iocb into the context's free list */
 		spin_lock_irq(&ctx->ctx_lock);
@@ -527,12 +528,14 @@ static void aio_fput_routine(struct work_struct *data)
  */
 static int __aio_put_req(struct kioctx *ctx, struct kiocb *req)
 {
+	int schedule_putreq = 0;
+
 	dprintk(KERN_DEBUG "aio_put(%p): f_count=%ld\n",
 		req, atomic_long_read(&req->ki_filp->f_count));
 
 	assert_spin_locked(&ctx->ctx_lock);
 
-	req->ki_users --;
+	req->ki_users--;
 	BUG_ON(req->ki_users < 0);
 	if (likely(req->ki_users))
 		return 0;
@@ -540,10 +543,23 @@ static int __aio_put_req(struct kioctx *ctx, struct kiocb *req)
 	req->ki_cancel = NULL;
 	req->ki_retry = NULL;
 
-	/* Must be done under the lock to serialise against cancellation.
-	 * Call this aio_fput as it duplicates fput via the fput_work.
+	/*
+	 * Try to optimize the aio and eventfd file* puts, by avoiding to
+	 * schedule work in case it is not __fput() time. In normal cases,
+	 * we would not be holding the last reference to the file*, so
+	 * this function will be executed w/out any aio kthread wakeup.
 	 */
-	if (unlikely(atomic_long_dec_and_test(&req->ki_filp->f_count))) {
+	if (unlikely(atomic_long_dec_and_test(&req->ki_filp->f_count)))
+		schedule_putreq++;
+	else
+		req->ki_filp = NULL;
+	if (req->ki_eventfd != NULL) {
+		if (unlikely(atomic_long_dec_and_test(&req->ki_eventfd->f_count)))
+			schedule_putreq++;
+		else
+			req->ki_eventfd = NULL;
+	}
+	if (unlikely(schedule_putreq)) {
 		get_ioctx(ctx);
 		spin_lock(&fput_lock);
 		list_add(&req->ki_list, &fput_head);
@@ -1009,7 +1025,7 @@ int aio_complete(struct kiocb *iocb, long res, long res2)
 	 * eventfd. The eventfd_signal() function is safe to be called
 	 * from IRQ context.
 	 */
-	if (!IS_ERR(iocb->ki_eventfd))
+	if (iocb->ki_eventfd != NULL)
 		eventfd_signal(iocb->ki_eventfd, 1);
 
 put_rq:
@@ -1608,6 +1624,7 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
 		req->ki_eventfd = eventfd_fget((int) iocb->aio_resfd);
 		if (IS_ERR(req->ki_eventfd)) {
 			ret = PTR_ERR(req->ki_eventfd);
+			req->ki_eventfd = NULL;
 			goto out_put_req;
 		}
 	}
--
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