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:

quoted

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.

quoted

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

quoted

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 <longli@microsoft.com>
---
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

quoted

   instead of a WARN_ON_ONCE() splat during a normal ifdown/MTU

change,

quoted

   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