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net: prevent torn reads in netdev_tc_txq

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netdev_set_tc_queue() (and related helpers/drivers such as
netdev_bind_sb_channel_queue(), netdev_reset_tc(), and
netdev_unbind_sb_channel()) perform separate 16-bit writes to
dev->tc_to_txq[tc].count and dev->tc_to_txq[tc].offset.

Furthermore, memset() in netdev_reset_tc() and
netdev_unbind_sb_channel() provides no guarantee of performing
full 32-bit word stores.

Concurrent lockless readers (e.g. skb_tx_hash(), netdev_txq_to_tc(),
ixgbe_select_queue(), taprio, mqprio, FPE drivers) can observe torn
values where offset and count belong to inconsistent configurations.

Redefine struct netdev_tc_txq to embed count and offset inside a union
with a u32 combined field, allowing atomic manipulation via
READ_ONCE() and WRITE_ONCE().

Update all lockless readers and writers across the kernel to use
READ_ONCE() and WRITE_ONCE() on the combined field.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260812085440.3917924-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet 2026-08-12 08:54:38 +00:00 • committed by Jakub Kicinski
commit 21ef2d065a
11 changed files with 94 additions and 43 deletions
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