netfs: zero the tail of a short DIO/unbuffered readgrafted

The buffered read collector zero-fills the tail of a short read that
stops below the inode's i_size (netfs_clear_unread()), so a read that
races an extending write still returns the expected number of bytes.
The non-buffered collector path does no such thing: it just records
how much was transferred.

Add the same zero-fill for the non-buffered case, gated on
NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short
result from it is known to be safe to treat as a hole, as opposed to
NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of
the file and should be reported short as-is. Only CLEAR_TAIL should
zero-fill here; a real EOF must stay a real short read.

No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest,
so this is inert on its own -- a following change teaches cifs to set
it in the one case that needs it.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

1 files changed, 154 insertions, 0 deletions

diff --git a/drivers/gpu/host1x/fence.c b/drivers/gpu/host1x/fence.c
new file mode 100644
index 000000000..b9a7d0bf9
--- /dev/null
+++ b/drivers/gpu/host1x/fence.c
@@ -0,0 +1,154 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Syncpoint dma_fence implementation
+ *
+ * Copyright (c) 2020, NVIDIA Corporation.
+ */
+
+#include <linux/dma-fence.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/slab.h>
+#include <linux/sync_file.h>
+
+#include "fence.h"
+#include "intr.h"
+#include "syncpt.h"
+
+static const char *host1x_syncpt_fence_get_driver_name(struct dma_fence *f)
+{
+	return "host1x";
+}
+
+static const char *host1x_syncpt_fence_get_timeline_name(struct dma_fence *f)
+{
+	return "syncpoint";
+}
+
+static struct host1x_syncpt_fence *to_host1x_fence(struct dma_fence *f)
+{
+	return container_of(f, struct host1x_syncpt_fence, base);
+}
+
+static bool host1x_syncpt_fence_enable_signaling(struct dma_fence *f)
+{
+	struct host1x_syncpt_fence *sf = to_host1x_fence(f);
+
+	if (host1x_syncpt_is_expired(sf->sp, sf->threshold))
+		return false;
+
+	/* Reference for interrupt path. */
+	dma_fence_get(f);
+
+	/*
+	 * The dma_fence framework requires the fence driver to keep a
+	 * reference to any fences for which 'enable_signaling' has been
+	 * called (and that have not been signalled).
+	 *
+	 * We cannot currently always guarantee that all fences get signalled
+	 * or cancelled. As such, for such situations, set up a timeout, so
+	 * that long-lasting fences will get reaped eventually.
+	 */
+	if (sf->timeout) {
+		/* Reference for timeout path. */
+		dma_fence_get(f);
+		schedule_delayed_work(&sf->timeout_work, msecs_to_jiffies(30000));
+	}
+
+	host1x_intr_add_fence_locked(sf->sp->host, sf);
+
+	/*
+	 * The fence may get signalled at any time after the above call,
+	 * so we need to initialize all state used by signalling
+	 * before it.
+	 */
+
+	return true;
+}
+
+static const struct dma_fence_ops host1x_syncpt_fence_ops = {
+	.get_driver_name = host1x_syncpt_fence_get_driver_name,
+	.get_timeline_name = host1x_syncpt_fence_get_timeline_name,
+	.enable_signaling = host1x_syncpt_fence_enable_signaling,
+};
+
+void host1x_fence_signal(struct host1x_syncpt_fence *f)
+{
+	if (atomic_xchg(&f->signaling, 1)) {
+		/*
+		 * Already on timeout path, but we removed the fence before
+		 * timeout path could, so drop interrupt path reference.
+		 */
+		dma_fence_put(&f->base);
+		return;
+	}
+
+	if (f->timeout && cancel_delayed_work(&f->timeout_work)) {
+		/*
+		 * We know that the timeout path will not be entered.
+		 * Safe to drop the timeout path's reference now.
+		 */
+		dma_fence_put(&f->base);
+	}
+
+	dma_fence_signal_locked(&f->base);
+	dma_fence_put(&f->base);
+}
+
+static void do_fence_timeout(struct work_struct *work)
+{
+	struct delayed_work *dwork = (struct delayed_work *)work;
+	struct host1x_syncpt_fence *f =
+		container_of(dwork, struct host1x_syncpt_fence, timeout_work);
+
+	if (atomic_xchg(&f->signaling, 1)) {
+		/* Already on interrupt path, drop timeout path reference if any. */
+		if (f->timeout)
+			dma_fence_put(&f->base);
+		return;
+	}
+
+	if (host1x_intr_remove_fence(f->sp->host, f)) {
+		/*
+		 * Managed to remove fence from queue, so it's safe to drop
+		 * the interrupt path's reference.
+		 */
+		dma_fence_put(&f->base);
+	}
+
+	dma_fence_set_error(&f->base, -ETIMEDOUT);
+	dma_fence_signal(&f->base);
+	if (f->timeout)
+		dma_fence_put(&f->base);
+}
+
+struct dma_fence *host1x_fence_create(struct host1x_syncpt *sp, u32 threshold,
+				      bool timeout)
+{
+	struct host1x_syncpt_fence *fence;
+
+	fence = kzalloc_obj(*fence);
+	if (!fence)
+		return ERR_PTR(-ENOMEM);
+
+	fence->sp = sp;
+	fence->threshold = threshold;
+	fence->timeout = timeout;
+
+	dma_fence_init(&fence->base, &host1x_syncpt_fence_ops, &sp->fences.lock,
+		       dma_fence_context_alloc(1), 0);
+
+	INIT_DELAYED_WORK(&fence->timeout_work, do_fence_timeout);
+
+	return &fence->base;
+}
+EXPORT_SYMBOL(host1x_fence_create);
+
+void host1x_fence_cancel(struct dma_fence *f)
+{
+	struct host1x_syncpt_fence *sf = to_host1x_fence(f);
+
+	schedule_delayed_work(&sf->timeout_work, 0);
+	flush_delayed_work(&sf->timeout_work);
+}
+EXPORT_SYMBOL(host1x_fence_cancel);