Hi Alex,
On Monday, August 16, 2021 4:46:08 PM CEST Alex Elder wrote:
> 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>...).
I'm going to remove that tag and send a v3. I too had doubts about using it in
this case and I was about to omit it (please consider I have just a few months
of experience with kernel hacking and, as far as I can remember, I haven't had
more than one other occasion to deal with the kernel test robot).
Now I think I understand when I should use the Reported-by tag and I'll use it
accordingly to what you and the others explained in this thread.
> > ---
> >
> > 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.
Yes, sure.
>
> > #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 didn't notice that addition (it was not intentional). I'll delete
the line in v3.
> 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
I've configured an automatic run of checkpatch.pl a long time ago. It runs
(automatically) every time I save a "git commit -s -v". Unfortunately,
sometimes happens that I'm distracted by something else and I don't see its
output (at least I don't read it in its entirety). My fault, obviously. I'll
be more focused on what I'm doing when I'm working on the next patches.
> 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.
As said above, I have little experience. So, believe me, I don't minimally
trust my own code and I wouldn't dare to submit patches without building with
"make C=2 -j8 drivers/staging/greybus/ W=1".
I'm not entirely sure of what happened, because I ran make at least a couple
of times, maybe more. I suppose it has to do with some greybus related options
in .config that only this evening I noticed I had to enable. When today I ran
"make menuconfig" I saw that a couple of them were not set but I can't
remember which.
Now that they are set, GCC fails with the v1 of my patch (downloaded and
installed on a new test branch based on Greg's staging-testing). Yesterday it
didn't fail.
> > 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.
Correct, I should have made it since v1. This will also go in v3.
> > + 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[] = {
Thanks for your kind review and the time you spent on it.
Regards,
Fabio
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