BUG: commit "ARM: Remove __ARCH_WANT_INTERRUPTS_ON_CTXSW on pre-ARMv6 CPUs" breaks armv5 with CONFIG_PREEMPT

Hello Catalin,

on current linus/master on armv5 we observed stack trashing[1] on high
load. I bisected this problem down to commit:

b9d4d42ad901cc848ac87f1cb8923fded3645568 is the first bad commit
commit b9d4d42ad901cc848ac87f1cb8923fded3645568
Author: Catalin Marinas [off-list ref]
Date:   Mon Nov 28 21:57:24 2011 +0000

    ARM: Remove __ARCH_WANT_INTERRUPTS_ON_CTXSW on pre-ARMv6 CPUs

    This patch removes the __ARCH_WANT_INTERRUPTS_ON_CTXSW definition for
    ARMv5 and earlier processors. On such processors, the context switch
    requires a full cache flush. To avoid high interrupt latencies, this
    patch defers the mm switching to the post-lock switch hook if the
    interrupts are disabled.

    Reviewed-by: Will Deacon [off-list ref]
    Tested-by: Will Deacon [off-list ref]
    Reviewed-by: Frank Rowand [off-list ref]
    Tested-by: Marc Zyngier [off-list ref]
    Signed-off-by: Catalin Marinas [off-list ref]

:040000 040000 034899bdcbc9aa59b5455a85a9d78b646b4cf784 ecc23e33a4ca807d4153f87fbea85a9437ff2928 M      arch

The problem can be reproduced on several mx28 and an at91sam9263 and
only occurs of CONFIG_PREEMPT (Preemptible Kernel (Low-Latency Desktop))
is enabled.

I have the gut feeling that the "if (irqs_disabled())" check in the
above patch is not correct for CONFIG_PREEMPT.

Marc

[1] The test program creating 150 threads in a row crashes like this:

[8]+  Segmentation fault         ./thread_test_c
[5]   Illegal instruction        ./thread_test_c
[4]   Illegal instruction        ./thread_test_c
[2]   Segmentation fault         ./thread_test_c
[3]   Illegal instruction        ./thread_test_c
[1]   Segmentation fault         ./thread_test_c

-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
Industrial Linux Solutions        | Phone: +49-231-2826-924     |
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