Hi!

I tried to prepare next 4.4-rt release. I have code ready, but while
running tests I realized that only two targets are used to run them.

We 4.19-rt has known bugs breaking boot on de0-nano (and probably
other) boards, and according to code inspection, same bug is present
in 4.4-rt. Fix is not complex, but I'm not comfortable applying it
without _any_ testing.

If I'm right, 4.4-rt should be broken on socfpga boards (arm32) in
non-realtime configuration; it should panic on boot in cca 50% of
cases. Patch below should fix it.

Best regards,
								Pavel

commit 20124aef8572b764ffd90d836253153102c763c5
Author: Pavel Machek [off-list ref]
Date:   Sat Mar 21 22:58:43 2020 +0100

    With -rt tree but prempt-rt not enabled, de0-nano was getting failures
    during boot, such as this:
    
    https://lava.ciplatform.org/scheduler/job/13037
    
    [    6.813352] Freeing unused kernel memory: 1024K
    [    6.817927] Unable to handle kernel paging request at virtual address e7fddef0
    [    6.825121] pgd = (ptrval)
    [    6.827816] [e7fddef0] *pgd=27e1141e(bad)
    [    6.831818] Internal error: Oops: 8000000d [#1] SMP ARM
    [    6.837019] Modules linked in:
    [    6.840067] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.19.106-cip21-gc82fe0af5 #1
    [    6.847601] Hardware name: Altera SOCFPGA
    [    6.851596] PC is at 0xe7fddef0
    [    6.854733] LR is at irq_work_run_list+0x84/0xc0
    
    Bisect revealed fc9f4631a290 is the problematic commit, and some code
    auditing revealed that it is working with wrong list. Fix it.
    
    Signed-off-by: Pavel Machek [off-list ref]
    Fixes: fc9f4631a290 ("irqwork: push most work into softirq context")

diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index 2899ba0d23d1..19896e6f1b2a 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c

@@ -78,7 +78,8 @@ bool irq_work_queue_on(struct irq_work *work, int cpu)
 	if (!irq_work_claim(work))
 		return false;
 
-	if (IS_ENABLED(CONFIG_PREEMPT_RT_FULL) && !(work->flags & IRQ_WORK_HARD_IRQ))
+	if ((IS_ENABLED(CONFIG_PREEMPT_RT_FULL) && !(work->flags & IRQ_WORK_HARD_IRQ))
+	    || (work->flags & IRQ_WORK_LAZY))
 		list = &per_cpu(lazy_list, cpu);
 	else
 		list = &per_cpu(raised_list, cpu);

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html