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commit 7c686eff39acbfdcba2d444c4a4430ae6cf74d4e
Author: David Bidner <[email protected]>
Date: Mon Oct 12 20:27:26 2026 +0200
libdde_linux26: Make the softirq pending word updates atomic
DDE runs each Linux "cpu" as CPU 0 in separate threads and its
local_irq_save() only disables interrupts on the current thread, so the
softirq pending word (irq_stat[0].__softirq_pending) is shared without
real mutual exclusion. __raise_softirq_irqoff() expands to a plain
read-modify-write (local_softirq_pending() |= bit) and __do_softirq()
clears the word with a plain store, so a raise can be lost:
- the IRQ thread raises NET_RX from __napi_schedule();
- the networking threads raise NET_TX via raise_softirq_irqoff();
- the softirq thread reads the word and then clears it.
A NET_RX raise that lands between the softirq thread's read and its
clear (or between two plain |= operations) is overwritten. The NAPI
entry stays on the poll list but no softirq is pending, so the softirq
thread blocks on dde_softirq_sem and the network stack stops.
Make the raise and the read-and-clear atomic: dde_or_softirq_pending()
uses __sync_fetch_and_or() and dde_softirq_pending_xchg() uses
__sync_lock_test_and_set(..., 0); __raise_softirq_irqoff() and
__do_softirq() use them.
* libdde_linux26/contrib/include/linux/interrupt.h: declare the helpers
and use dde_or_softirq_pending() in __raise_softirq_irqoff().
* libdde_linux26/lib/src/arch/l4/softirq.c (__do_softirq): read and
clear the pending word atomically.
Message-ID: <[email protected]>
commit b8869c337e9d0d6db372e687de3ee7573fc1bdc9
Author: David Bidner <[email protected]>
Date: Mon Oct 12 20:27:25 2026 +0200
libdde_linux26: Wake the softirq thread when __do_softirq gives up
DDE's __do_softirq() runs a bounded retry loop and returns when the
softirq pending bits are still set after MAX_SOFTIRQ_RETRIES. Linux
wakes ksoftirqd at that point; DDE has no such helper, so the softirq
thread immediately blocks again on dde_softirq_sem and the pending work
is never processed.
Post dde_softirq_sem before returning when softirqs are still pending,
mirroring mainline's wakeup_softirqd().
* libdde_linux26/lib/src/arch/l4/softirq.c (__do_softirq): Wake the
softirq thread if pending work remains.
Message-ID: <[email protected]>
-----------------------------------------------------------------------
Summary of changes:
libdde_linux26/contrib/include/linux/interrupt.h | 7 ++++++-
libdde_linux26/lib/src/arch/l4/softirq.c | 18 ++++++++++++++----
2 files changed, 20 insertions(+), 5 deletions(-)
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