Date:   Mon, 23 May 2022 10:05:18 +0200
From:   Íñigo Huguet <ihuguet@...hat.com>
To:     Íñigo Huguet <ihuguet@...hat.com>,
        Edward Cree <ecree.xilinx@...il.com>,
        bhutchings@...arflare.com, "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/2] sfc: simplify mtd partitions list handling

On Fri, May 13, 2022 at 10:02 AM Martin Habets <habetsm.xilinx@...il.com> wrote:
>
> On Wed, May 11, 2022 at 12:36:04PM +0200, Íñigo Huguet wrote:
> > efx_mtd_partitions are embedded inside efx_mcdi_mtd_partition structs.
> > They contain a list entry that is appended to efx->mtd_list, which is
> > traversed to perform add/remove/rename/etc operations over all
> > efx_mtd_partitions.
> >
> > However, almost all operations done on a efx_mtd_partition asume that it
> > is actually embedded inside an efx_mcdi_mtd_partition, and the
> > deallocation asume that the first member of the list is located at the
> > beginning of the allocated memory.
> >
> > Given all that asumptions, the possibility of having an
> > efx_mtd_partition not embedded in an efx_mcdi_efx_partition doesn't
> > exist. Neither it does the possibility of being in a memory position
> > other the one allocated for the efx_mcdi_mtd_partition array. Also, they
> > never need to be reordered.
> >
> > Given all that, it is better to get rid of the list and use directly the
> > efx_mcdi_mtd_partition array. This shows more clearly how they lay
> > in memory, list traversal is more obvious and it save a small amount
> > of memory on the list nodes.
>
> I like this. Just 1 comment below.

I will prepare a new version, dropping the previous patch

>
> > Signed-off-by: Íñigo Huguet <ihuguet@...hat.com>
> > ---
> >  drivers/net/ethernet/sfc/ef10.c       | 12 ++++++--
> >  drivers/net/ethernet/sfc/efx.h        |  4 +--
> >  drivers/net/ethernet/sfc/efx_common.c |  3 --
> >  drivers/net/ethernet/sfc/mtd.c        | 42 ++++++++++-----------------
> >  drivers/net/ethernet/sfc/net_driver.h |  9 ++++--
> >  5 files changed, 33 insertions(+), 37 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/sfc/ef10.c b/drivers/net/ethernet/sfc/ef10.c
> > index 15a229731296..b5284fa529b7 100644
> > --- a/drivers/net/ethernet/sfc/ef10.c
> > +++ b/drivers/net/ethernet/sfc/ef10.c
> > @@ -3584,10 +3584,16 @@ static int efx_ef10_mtd_probe(struct efx_nic *efx)
> >               return 0;
> >       }
> >
> > -     rc = efx_mtd_add(efx, &parts[0].common, n_parts, sizeof(*parts));
> > -fail:
> > +     rc = efx_mtd_add(efx, parts, n_parts);
> >       if (rc)
> > -             kfree(parts);
> > +             goto fail;
> > +     efx->mcdi_mtd_parts = parts;
> > +     efx->n_mcdi_mtd_parts = n_parts;
> > +
> > +     return 0;
> > +
> > +fail:
> > +     kfree(parts);
> >       return rc;
> >  }
> >
> > diff --git a/drivers/net/ethernet/sfc/efx.h b/drivers/net/ethernet/sfc/efx.h
> > index c05a83da9e44..2ab9ba691b0d 100644
> > --- a/drivers/net/ethernet/sfc/efx.h
> > +++ b/drivers/net/ethernet/sfc/efx.h
> > @@ -181,8 +181,8 @@ void efx_update_sw_stats(struct efx_nic *efx, u64 *stats);
> >
> >  /* MTD */
> >  #ifdef CONFIG_SFC_MTD
> > -int efx_mtd_add(struct efx_nic *efx, struct efx_mtd_partition *parts,
> > -             size_t n_parts, size_t sizeof_part);
> > +int efx_mtd_add(struct efx_nic *efx, struct efx_mcdi_mtd_partition *parts,
> > +             size_t n_parts);
> >  static inline int efx_mtd_probe(struct efx_nic *efx)
> >  {
> >       return efx->type->mtd_probe(efx);
> > diff --git a/drivers/net/ethernet/sfc/efx_common.c b/drivers/net/ethernet/sfc/efx_common.c
> > index f6577e74d6e6..8802790403e9 100644
> > --- a/drivers/net/ethernet/sfc/efx_common.c
> > +++ b/drivers/net/ethernet/sfc/efx_common.c
> > @@ -987,9 +987,6 @@ int efx_init_struct(struct efx_nic *efx,
> >       INIT_LIST_HEAD(&efx->node);
> >       INIT_LIST_HEAD(&efx->secondary_list);
> >       spin_lock_init(&efx->biu_lock);
> > -#ifdef CONFIG_SFC_MTD
> > -     INIT_LIST_HEAD(&efx->mtd_list);
> > -#endif
> >       INIT_WORK(&efx->reset_work, efx_reset_work);
> >       INIT_DELAYED_WORK(&efx->monitor_work, efx_monitor);
> >       efx_selftest_async_init(efx);
> > diff --git a/drivers/net/ethernet/sfc/mtd.c b/drivers/net/ethernet/sfc/mtd.c
> > index 273c08e5455f..4d06e8a9a729 100644
> > --- a/drivers/net/ethernet/sfc/mtd.c
> > +++ b/drivers/net/ethernet/sfc/mtd.c
> > @@ -12,6 +12,7 @@
> >
> >  #include "net_driver.h"
> >  #include "efx.h"
> > +#include "mcdi.h"
> >
> >  #define to_efx_mtd_partition(mtd)                            \
> >       container_of(mtd, struct efx_mtd_partition, mtd)
> > @@ -48,18 +49,16 @@ static void efx_mtd_remove_partition(struct efx_mtd_partition *part)
> >               ssleep(1);
> >       }
> >       WARN_ON(rc);
> > -     list_del(&part->node);
> >  }
> >
> > -int efx_mtd_add(struct efx_nic *efx, struct efx_mtd_partition *parts,
> > -             size_t n_parts, size_t sizeof_part)
> > +int efx_mtd_add(struct efx_nic *efx, struct efx_mcdi_mtd_partition *parts,
> > +             size_t n_parts)
> >  {
> >       struct efx_mtd_partition *part;
> >       size_t i;
> >
> >       for (i = 0; i < n_parts; i++) {
> > -             part = (struct efx_mtd_partition *)((char *)parts +
> > -                                                 i * sizeof_part);
> > +             part = &parts[i].common;
> >
> >               part->mtd.writesize = 1;
> >
> > @@ -78,47 +77,38 @@ int efx_mtd_add(struct efx_nic *efx, struct efx_mtd_partition *parts,
> >
> >               if (mtd_device_register(&part->mtd, NULL, 0))
> >                       goto fail;
> > -
> > -             /* Add to list in order - efx_mtd_remove() depends on this */
> > -             list_add_tail(&part->node, &efx->mtd_list);
> >       }
> >
> >       return 0;
> >
> >  fail:
> > -     while (i--) {
> > -             part = (struct efx_mtd_partition *)((char *)parts +
> > -                                                 i * sizeof_part);
> > -             efx_mtd_remove_partition(part);
> > -     }
> > +     while (i--)
> > +             efx_mtd_remove_partition(&parts[i].common);
> > +
> >       /* Failure is unlikely here, but probably means we're out of memory */
> >       return -ENOMEM;
> >  }
> >
> >  void efx_mtd_remove(struct efx_nic *efx)
> >  {
> > -     struct efx_mtd_partition *parts, *part, *next;
> > +     int i;
> >
> >       WARN_ON(efx_dev_registered(efx));
> >
> > -     if (list_empty(&efx->mtd_list))
> > -             return;
> > -
> > -     parts = list_first_entry(&efx->mtd_list, struct efx_mtd_partition,
> > -                              node);
> > +     for (i = 0; i < efx->n_mcdi_mtd_parts; i++)
> > +             efx_mtd_remove_partition(&efx->mcdi_mtd_parts[i].common);
> >
> > -     list_for_each_entry_safe(part, next, &efx->mtd_list, node)
> > -             efx_mtd_remove_partition(part);
> > -
> > -     kfree(parts);
> > +     kfree(efx->mcdi_mtd_parts);
> > +     efx->mcdi_mtd_parts = NULL;
> > +     efx->n_mcdi_mtd_parts = 0;
>
> It is safer to first set to NULL/0 before freeing the memory.
> With this sequence bad things can happen if the thread gets descheduled
> right after the kfree.

To prevent this we'd also need to use memory barriers. I don't think
we need them because all usages of these fields are done under the
rtnl lock. I won't apply this change in the new version because I find
it useless, but please explain me the reason if you disagree.

>
> Martin
>
> >  }
> >
> >  void efx_mtd_rename(struct efx_nic *efx)
> >  {
> > -     struct efx_mtd_partition *part;
> > +     int i;
> >
> >       ASSERT_RTNL();
> >
> > -     list_for_each_entry(part, &efx->mtd_list, node)
> > -             efx->type->mtd_rename(part);
> > +     for (i = 0; i < efx->n_mcdi_mtd_parts; i++)
> > +             efx->type->mtd_rename(&efx->mcdi_mtd_parts[i].common);
> >  }
> > diff --git a/drivers/net/ethernet/sfc/net_driver.h b/drivers/net/ethernet/sfc/net_driver.h
> > index 318db906a154..5d20b25b0e82 100644
> > --- a/drivers/net/ethernet/sfc/net_driver.h
> > +++ b/drivers/net/ethernet/sfc/net_driver.h
> > @@ -107,6 +107,8 @@ struct hwtstamp_config;
> >
> >  struct efx_self_tests;
> >
> > +struct efx_mcdi_mtd_partition;
> > +
> >  /**
> >   * struct efx_buffer - A general-purpose DMA buffer
> >   * @addr: host base address of the buffer
> > @@ -865,7 +867,8 @@ enum efx_xdp_tx_queues_mode {
> >   * @irq_zero_count: Number of legacy IRQs seen with queue flags == 0
> >   * @irq_level: IRQ level/index for IRQs not triggered by an event queue
> >   * @selftest_work: Work item for asynchronous self-test
> > - * @mtd_list: List of MTDs attached to the NIC
> > + * @mcdi_mtd_parts: Array of MTDs attached to the NIC
> > + * @n_mcdi_mtd_parts: Number of MTDs attached to the NIC
> >   * @nic_data: Hardware dependent state
> >   * @mcdi: Management-Controller-to-Driver Interface state
> >   * @mac_lock: MAC access lock. Protects @port_enabled, @phy_mode,
> > @@ -1033,7 +1036,8 @@ struct efx_nic {
> >       struct delayed_work selftest_work;
> >
> >  #ifdef CONFIG_SFC_MTD
> > -     struct list_head mtd_list;
> > +     struct efx_mcdi_mtd_partition *mcdi_mtd_parts;
> > +     unsigned int n_mcdi_mtd_parts;
> >  #endif
> >
> >       void *nic_data;
> > @@ -1134,7 +1138,6 @@ static inline unsigned int efx_port_num(struct efx_nic *efx)
> >  }
> >
> >  struct efx_mtd_partition {
> > -     struct list_head node;
> >       struct mtd_info mtd;
> >       const char *dev_type_name;
> >       const char *type_name;
> > --
> > 2.34.1
>


-- 
Íñigo Huguet

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