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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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