Re: [PATCH v2] staging: greybus: Convert uart.c from IDR to XArray

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On 8/14/21 1:11 PM, Fabio M. De Francesco wrote:
Convert greybus/uart.c from IDR to XArray. The abstract data type XArray
is more memory-efficient, parallelisable, and cache friendly. It takes
advantage of RCU to perform lookups without locking. Furthermore, IDR is
deprecated because XArray has a better (cleaner and more consistent) API.

I haven't verified the use of the new API (yet) but I have a few
comments on your patch, below.

					-Alex

Reported-by: kernel test robot <lkp@xxxxxxxxx>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx>

I'm not sure I'm right about this...  But the actual change you're
making has nothing to do with what the Intel test robot reported.
I personally find the "Reported-by" here a little misleading, but
maybe the "Link" line that gets added will provide explanation.

Anyway, unless someone else contradicts/corrects me, I'd rather
not have the "Reported-by" here (despite wanting to provide much
credit to <lkp@xxxxxxxxx>...).

---

v1->v2:
         Fixed an issue found by the kernel test robot. It was due to
         passing to xa_*lock() the same old mutex that IDR used with
         the previous version of the code.

  drivers/staging/greybus/uart.c | 29 ++++++++++++++---------------
  1 file changed, 14 insertions(+), 15 deletions(-)

diff --git a/drivers/staging/greybus/uart.c b/drivers/staging/greybus/uart.c
index 73f01ed1e5b7..5bf993e40f84 100644
--- a/drivers/staging/greybus/uart.c
+++ b/drivers/staging/greybus/uart.c
@@ -22,7 +22,7 @@
  #include <linux/serial.h>
  #include <linux/tty_driver.h>
  #include <linux/tty_flip.h>
-#include <linux/idr.h>
+#include <linux/xarray.h>
  #include <linux/fs.h>
  #include <linux/kdev_t.h>
  #include <linux/kfifo.h>
@@ -33,6 +33,7 @@
  #include "gbphy.h"
#define GB_NUM_MINORS 16 /* 16 is more than enough */
+#define GB_RANGE_MINORS		XA_LIMIT(0, GB_NUM_MINORS)
  #define GB_NAME		"ttyGB"

Please align the right-hand side of all three definitions here.

  #define GB_UART_WRITE_FIFO_SIZE		PAGE_SIZE
@@ -67,8 +68,7 @@ struct gb_tty {
  };
static struct tty_driver *gb_tty_driver;
-static DEFINE_IDR(tty_minors);
-static DEFINE_MUTEX(table_lock);
+static DEFINE_XARRAY(tty_minors);
static int gb_uart_receive_data_handler(struct gb_operation *op)
  {
@@ -77,6 +77,7 @@ static int gb_uart_receive_data_handler(struct gb_operation *op)
  	struct tty_port *port = &gb_tty->port;
  	struct gb_message *request = op->request;
  	struct gb_uart_recv_data_request *receive_data;
+

Please do not add a blank line amid the local variable
definitions.

I'm not sure it checks for this, but you should run
your patch through "checkpatch.pl" before you send
it.  E.g.:
    ./scripts/checkpatch.pl idr_to_xarray.patch

The error reported in the build of your first version
of this patch makes me think you might not have test-
built the code.  I don't know if that's the case, but
(at least) building the code is expected before you
submit a patch for review.

  	u16 recv_data_size;
  	int count;
  	unsigned long tty_flags = TTY_NORMAL;
@@ -341,8 +342,8 @@ static struct gb_tty *get_gb_by_minor(unsigned int minor)
  {
  	struct gb_tty *gb_tty;
- mutex_lock(&table_lock);
-	gb_tty = idr_find(&tty_minors, minor);
+	xa_lock(&tty_minors);
+	gb_tty = xa_load(&tty_minors, minor);
  	if (gb_tty) {
  		mutex_lock(&gb_tty->mutex);
  		if (gb_tty->disconnected) {
@@ -353,19 +354,19 @@ static struct gb_tty *get_gb_by_minor(unsigned int minor)
  			mutex_unlock(&gb_tty->mutex);
  		}
  	}
-	mutex_unlock(&table_lock);
+	xa_unlock(&tty_minors);
  	return gb_tty;
  }
static int alloc_minor(struct gb_tty *gb_tty)
  {
  	int minor;
+	int ret;
- mutex_lock(&table_lock);
-	minor = idr_alloc(&tty_minors, gb_tty, 0, GB_NUM_MINORS, GFP_KERNEL);
-	mutex_unlock(&table_lock);
-	if (minor >= 0)
-		gb_tty->minor = minor;
+	ret = xa_alloc(&tty_minors, &minor, gb_tty, GB_RANGE_MINORS, GFP_KERNEL);
+	if (ret)
+		return ret;

The caller of alloc_minor() (gb_uart_probe()) checks the return
value, and if it's -ENOSPC it logs a device error indicating
there are no remaining free device minor numbers.  For xa_alloc()
this is indicated by returning -EBUSY.  Please update the caller
to print the error message based on the updated error code.

+	gb_tty->minor = minor;
  	return minor;
  }
@@ -374,9 +375,7 @@ static void release_minor(struct gb_tty *gb_tty)
  	int minor = gb_tty->minor;
gb_tty->minor = 0; /* Maybe should use an invalid value instead */
-	mutex_lock(&table_lock);
-	idr_remove(&tty_minors, minor);
-	mutex_unlock(&table_lock);
+	xa_erase(&tty_minors, minor);
  }
static int gb_tty_install(struct tty_driver *driver, struct tty_struct *tty)
@@ -982,7 +981,7 @@ static void gb_tty_exit(void)
  {
  	tty_unregister_driver(gb_tty_driver);
  	put_tty_driver(gb_tty_driver);
-	idr_destroy(&tty_minors);
+	xa_destroy(&tty_minors);
  }
static const struct gbphy_device_id gb_uart_id_table[] = {






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