net: add helper to pre-check if PP for an Rx queue will be unreadable

mlx5 pokes into the rxq state to check if the queue has a memory
provider, and therefore whether it may produce unreadable mem.

net: add helper to pre-check if PP for an Rx queue will be unreadable

mlx5 pokes into the rxq state to check if the queue has a memory
provider, and therefore whether it may produce unreadable mem.
Add a helper for doing this in the page pool API. fbnic will want
a similar thing (tho, for a slightly different reason).

Reviewed-by: Mina Almasry <almasrymina@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Link: https://patch.msgid.link/20250901211214.1027927-11-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

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net: page_pool: add page_pool_get()

There is a page_pool_put() function but no get equivalent.
Having multiple references to a page pool is quite useful.
It avoids branching in create / destroy path

net: page_pool: add page_pool_get()

There is a page_pool_put() function but no get equivalent.
Having multiple references to a page pool is quite useful.
It avoids branching in create / destroy paths in drivers
which support memory providers.

Use the new helper in bnxt.

Acked-by: Jesper Dangaard Brouer <hawk@kernel.org>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Mina Almasry <almasrymina@google.com>
Link: https://patch.msgid.link/20250820025704.166248-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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net: page_pool: allow enabling recycling late, fix false positive warning

Page pool can have pages "directly" (locklessly) recycled to it,
if the NAPI that owns the page pool is scheduled to run on

net: page_pool: allow enabling recycling late, fix false positive warning

Page pool can have pages "directly" (locklessly) recycled to it,
if the NAPI that owns the page pool is scheduled to run on the same CPU.
To make this safe we check that the NAPI is disabled while we destroy
the page pool. In most cases NAPI and page pool lifetimes are tied
together so this happens naturally.

The queue API expects the following order of calls:
-> mem_alloc
alloc new pp
-> stop
napi_disable
-> start
napi_enable
-> mem_free
free old pp

Here we allocate the page pool in ->mem_alloc and free in ->mem_free.
But the NAPIs are only stopped between ->stop and ->start. We created
page_pool_disable_direct_recycling() to safely shut down the recycling
in ->stop. This way the page_pool_destroy() call in ->mem_free doesn't
have to worry about recycling any more.

Unfortunately, the page_pool_disable_direct_recycling() is not enough
to deal with failures which necessitate freeing the _new_ page pool.
If we hit a failure in ->mem_alloc or ->stop the new page pool has
to be freed while the NAPI is active (assuming driver attaches the
page pool to an existing NAPI instance and doesn't reallocate NAPIs).

Freeing the new page pool is technically safe because it hasn't been
used for any packets, yet, so there can be no recycling. But the check
in napi_assert_will_not_race() has no way of knowing that. We could
check if page pool is empty but that'd make the check much less likely
to trigger during development.

Add page_pool_enable_direct_recycling(), pairing with
page_pool_disable_direct_recycling(). It will allow us to create the new
page pools in "disabled" state and only enable recycling when we know
the reconfig operation will not fail.

Coincidentally it will also let us re-enable the recycling for the old
pool, if the reconfig failed:

-> mem_alloc (new)
-> stop (old)
# disables direct recycling for old
-> start (new)
# fail!!
-> start (old)
# go back to old pp but direct recycling is lost :(
-> mem_free (new)

The new helper is idempotent to make the life easier for drivers,
which can operate in HDS mode and support zero-copy Rx.
The driver can call the helper twice whether there are two pools
or it has multiple references to a single pool.

Fixes: 40eca00ae605 ("bnxt_en: unlink page pool when stopping Rx queue")
Tested-by: David Wei <dw@davidwei.uk>
Link: https://patch.msgid.link/20250805003654.2944974-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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