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, 189 insertions, 0 deletions

diff --git a/drivers/clocksource/timer-cs5535.c b/drivers/clocksource/timer-cs5535.c
new file mode 100644
index 000000000..8af666c39
--- /dev/null
+++ b/drivers/clocksource/timer-cs5535.c
@@ -0,0 +1,189 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Clock event driver for the CS5535/CS5536
+ *
+ * Copyright (C) 2006, Advanced Micro Devices, Inc.
+ * Copyright (C) 2007  Andres Salomon <dilinger@debian.org>
+ * Copyright (C) 2009  Andres Salomon <dilinger@collabora.co.uk>
+ *
+ * The MFGPTs are documented in AMD Geode CS5536 Companion Device Data Book.
+ */
+
+#include <linux/kernel.h>
+#include <linux/irq.h>
+#include <linux/interrupt.h>
+#include <linux/module.h>
+#include <linux/cs5535.h>
+#include <linux/clockchips.h>
+
+#define DRV_NAME "cs5535-clockevt"
+
+static int timer_irq;
+module_param_hw_named(irq, timer_irq, int, irq, 0644);
+MODULE_PARM_DESC(irq, "Which IRQ to use for the clock source MFGPT ticks.");
+
+/*
+ * We are using the 32.768kHz input clock - it's the only one that has the
+ * ranges we find desirable.  The following table lists the suitable
+ * divisors and the associated Hz, minimum interval and the maximum interval:
+ *
+ *  Divisor   Hz      Min Delta (s)  Max Delta (s)
+ *   1        32768   .00048828125      2.000
+ *   2        16384   .0009765625       4.000
+ *   4         8192   .001953125        8.000
+ *   8         4096   .00390625        16.000
+ *   16        2048   .0078125         32.000
+ *   32        1024   .015625          64.000
+ *   64         512   .03125          128.000
+ *  128         256   .0625           256.000
+ *  256         128   .125            512.000
+ */
+
+static struct cs5535_mfgpt_timer *cs5535_event_clock;
+
+/* Selected from the table above */
+
+#define MFGPT_DIVISOR 16
+#define MFGPT_SCALE  4     /* divisor = 2^(scale) */
+#define MFGPT_HZ  (32768 / MFGPT_DIVISOR)
+#define MFGPT_PERIODIC (MFGPT_HZ / HZ)
+
+/*
+ * The MFGPT timers on the CS5536 provide us with suitable timers to use
+ * as clock event sources - not as good as a HPET or APIC, but certainly
+ * better than the PIT.  This isn't a general purpose MFGPT driver, but
+ * a simplified one designed specifically to act as a clock event source.
+ * For full details about the MFGPT, please consult the CS5536 data sheet.
+ */
+
+static void disable_timer(struct cs5535_mfgpt_timer *timer)
+{
+	/* avoid races by clearing CMP1 and CMP2 unconditionally */
+	cs5535_mfgpt_write(timer, MFGPT_REG_SETUP,
+			(uint16_t) ~MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP1 |
+				MFGPT_SETUP_CMP2);
+}
+
+static void start_timer(struct cs5535_mfgpt_timer *timer, uint16_t delta)
+{
+	cs5535_mfgpt_write(timer, MFGPT_REG_CMP2, delta);
+	cs5535_mfgpt_write(timer, MFGPT_REG_COUNTER, 0);
+
+	cs5535_mfgpt_write(timer, MFGPT_REG_SETUP,
+			MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP2);
+}
+
+static int mfgpt_shutdown(struct clock_event_device *evt)
+{
+	disable_timer(cs5535_event_clock);
+	return 0;
+}
+
+static int mfgpt_set_periodic(struct clock_event_device *evt)
+{
+	disable_timer(cs5535_event_clock);
+	start_timer(cs5535_event_clock, MFGPT_PERIODIC);
+	return 0;
+}
+
+static int mfgpt_next_event(unsigned long delta, struct clock_event_device *evt)
+{
+	start_timer(cs5535_event_clock, delta);
+	return 0;
+}
+
+static struct clock_event_device cs5535_clockevent = {
+	.name = DRV_NAME,
+	.features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
+	.set_state_shutdown = mfgpt_shutdown,
+	.set_state_periodic = mfgpt_set_periodic,
+	.set_state_oneshot = mfgpt_shutdown,
+	.tick_resume = mfgpt_shutdown,
+	.set_next_event = mfgpt_next_event,
+	.rating = 250,
+	.owner = THIS_MODULE,
+};
+
+static irqreturn_t mfgpt_tick(int irq, void *dev_id)
+{
+	uint16_t val = cs5535_mfgpt_read(cs5535_event_clock, MFGPT_REG_SETUP);
+
+	/* See if the interrupt was for us */
+	if (!(val & (MFGPT_SETUP_SETUP | MFGPT_SETUP_CMP2 | MFGPT_SETUP_CMP1)))
+		return IRQ_NONE;
+
+	/* Turn off the clock (and clear the event) */
+	disable_timer(cs5535_event_clock);
+
+	if (clockevent_state_detached(&cs5535_clockevent) ||
+	    clockevent_state_shutdown(&cs5535_clockevent))
+		return IRQ_HANDLED;
+
+	/* Clear the counter */
+	cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_COUNTER, 0);
+
+	/* Restart the clock in periodic mode */
+
+	if (clockevent_state_periodic(&cs5535_clockevent))
+		cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_SETUP,
+				MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP2);
+
+	cs5535_clockevent.event_handler(&cs5535_clockevent);
+	return IRQ_HANDLED;
+}
+
+static int __init cs5535_mfgpt_init(void)
+{
+	unsigned long flags = IRQF_NOBALANCING | IRQF_TIMER | IRQF_SHARED;
+	struct cs5535_mfgpt_timer *timer;
+	int ret;
+	uint16_t val;
+
+	timer = cs5535_mfgpt_alloc_timer(MFGPT_TIMER_ANY, MFGPT_DOMAIN_WORKING);
+	if (!timer) {
+		printk(KERN_ERR DRV_NAME ": Could not allocate MFGPT timer\n");
+		return -ENODEV;
+	}
+	cs5535_event_clock = timer;
+
+	/* Set up the IRQ on the MFGPT side */
+	if (cs5535_mfgpt_setup_irq(timer, MFGPT_CMP2, &timer_irq)) {
+		printk(KERN_ERR DRV_NAME ": Could not set up IRQ %d\n",
+				timer_irq);
+		goto err_timer;
+	}
+
+	/* And register it with the kernel */
+	ret = request_irq(timer_irq, mfgpt_tick, flags, DRV_NAME, timer);
+	if (ret) {
+		printk(KERN_ERR DRV_NAME ": Unable to set up the interrupt.\n");
+		goto err_irq;
+	}
+
+	/* Set the clock scale and enable the event mode for CMP2 */
+	val = MFGPT_SCALE | (3 << 8);
+
+	cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_SETUP, val);
+
+	/* Set up the clock event */
+	printk(KERN_INFO DRV_NAME
+		": Registering MFGPT timer as a clock event, using IRQ %d\n",
+		timer_irq);
+	clockevents_config_and_register(&cs5535_clockevent, MFGPT_HZ,
+					0xF, 0xFFFE);
+
+	return 0;
+
+err_irq:
+	cs5535_mfgpt_release_irq(cs5535_event_clock, MFGPT_CMP2, &timer_irq);
+err_timer:
+	cs5535_mfgpt_free_timer(cs5535_event_clock);
+	printk(KERN_ERR DRV_NAME ": Unable to set up the MFGPT clock source\n");
+	return -EIO;
+}
+
+module_init(cs5535_mfgpt_init);
+
+MODULE_AUTHOR("Andres Salomon <dilinger@queued.net>");
+MODULE_DESCRIPTION("CS5535/CS5536 MFGPT clock event driver");
+MODULE_LICENSE("GPL");