RE: [EXTERNAL] Re: [PATCH net v6 1/7] net: mana: RCU-protect gc->cq_table lookups against concurrent CQ destroy

> On Mon, Aug 10, 2026 at 07:38:15PM -0700, Long Li wrote:
> > The EQ interrupt handler (mana_gd_process_eqe) looks up the completing
> > CQ in gc->cq_table[cq_id] and runs its callback, concurrently with CQ
> > teardown on another CPU that clears the slot and frees the CQ.
> > cq_table was a plain pointer array freed with no grace period, so the
> > two race into a use-after-free:
> >
> >   CPU A (mana_gd_intr, hard IRQ)        CPU B (CQ destroy)
> >   ----------------------------------    ------------------------------
> >   cq = gc->cq_table[cq_id];  // valid
> >                                         gc->cq_table[id] = NULL;
> >                                         kfree(cq);          // freed
> >   cq->cq.callback(ctx, cq);  // use-after-free
> >
> > The handler's existing rcu_read_lock() only guards the per-IRQ EQ list
> > traversal; cq_table was never under any RCU contract, and a read-side
> > lock is inert unless the freer also defers the free past a grace period.
> >
> > Put cq_table under RCU: annotate the base pointer and entries __rcu,
> > read with rcu_dereference() in the handler, publish with
> > rcu_assign_pointer(), and on teardown clear the slot then
> > synchronize_rcu() before freeing the CQ.  The grace period blocks
> > until every in-flight handler has dropped the old pointer, so the kfree() can
> no longer race the callback.
> >
> > This fixes only the CQ lifetime (the use-after-free); it does not make
> > the cq_id bound trustworthy.  gc->max_num_cqs is still range-checked
> > outside the published table, and hardening that field against a
> > spoofed device value is a separate change.
> >
> > netdev teardown destroys a CQ per TX and per RX queue, so one grace
> > period each in mana_gd_destroy_cq() would serialize up to
> > 2 * MANA_MAX_NUM_QUEUES synchronize_rcu() calls under RTNL on
> every
> > ifdown, MTU change or ring/channel reconfigure.  Clear all of a port's
> > CQ slots first and take a single grace period per teardown instead:
> > mana_gd_unpublish_cq() clears a slot without waiting, and
> > mana_gd_destroy_cq() -- which still serves the single-CQ callers --
> > finds the slot already cleared and skips its own synchronize_rcu().
> >
> > Fixes: ca9c54d2d6a5 ("net: mana: Add a driver for Microsoft Azure
> > Network Adapter (MANA)")
> > Signed-off-by: Long Li <[email protected]>
> > ---
> > Changes in v6:
> >  - mana_gd_unpublish_cq() and mana_ib_remove_cq_cb() clear a cq_table
> >    slot only when it still points at the CQ being torn down, so the
> >    two-pass teardown cannot wipe an entry a concurrent RDMA CQ create
> >    recycled during the grace period.
> >  - mana_gd_process_eqe() drops an already-unpublished (NULL) slot
> quietly
> >    instead of a WARN_ON_ONCE() splat during a normal ifdown/MTU
> change,
> >    and reads gc->cq_table before gc->max_num_cqs with an smp_rmb()
> >    between them so a shrinking re-establish cannot pair a stale bound
> >    with a newly published, smaller table.
> >  - Documented the cq_table/max_num_cqs contract on the cq_table field
> >    instead of rewording the comment above max_num_cqs.
> >
> > Changes in v5:
> >  - No code changes since v4 (resend as a standalone thread).
> >
> > Changes in v4:
> >  - Replaced the per-CQ synchronize_rcu() in the netdev teardown paths
> >    with a two-pass quiesce/free that takes one grace period per
> >    teardown; mana_gd_unpublish_cq() splits the slot-clear from the grace
> >    period.
> >  - Snapshot cq->id and max_num_cqs with READ_ONCE() in
> >    mana_hwc_establish_channel() so one value sizes, bounds and indexes
> >    cq_table.
> >  - Corrected the gc->cq_table lifetime comment in gdma.h; rescoped the
> >    changelog to the use-after-free fix (the bound is patch 7).
> >
> >  drivers/infiniband/hw/mana/cq.c               |  51 ++++++-
> >  .../net/ethernet/microsoft/mana/gdma_main.c   |  65 +++++++--
> >  .../net/ethernet/microsoft/mana/hw_channel.c  |  29 ++--
> > drivers/net/ethernet/microsoft/mana/mana_en.c | 136 ++++++++++++++----
> >  include/net/mana/gdma.h                       |  37 ++++-
> >  5 files changed, 268 insertions(+), 50 deletions(-)
> 
> This patch is so bloated with AI that it is hard to read and difficult to justify
> such a large diff for a simple change, which all drivers experience that flow.
> 
> As a bare minimum. you need to reorder mana_ib_gd_destroy_cq(),
> mana_ib_destroy_queue(), and mana_ib_remove_cq_cb() so that HW objects
> are stopped before SW state is torn down.
> 
> And probably introduce get/put CQ primitives.
> 
> Thanks

I'll clean up and follow your suggestions on v7.

Thanks

Long