Re: [PATCH] RISC-V: Add CONFIG_PREEMPT=y to defconfig

[Palmer Dabbelt <palmer@sifive.com>]

On Wed, 02 Jan 2019 18:59:11 PST (-0800), deanbo422@gmail.com wrote:
> Palmer Dabbelt <palmer@sifive.com> 於 2018年12月27日 週四 上午1:19寫道：
>>
>> On Tue, 25 Dec 2018 19:23:50 PST (-0800), linux@roeck-us.net wrote:
>> > On Wed, Dec 19, 2018 at 09:25:21PM -0800, Guenter Roeck wrote:
>> >> On Wed, Dec 19, 2018 at 05:45:11PM -0800, Guenter Roeck wrote:
>> >> > On Wed, Nov 21, 2018 at 10:58:05AM -0800, Palmer Dabbelt wrote:
>> >> > > I don't remember who suggested this, but I was talking to someone at
>> >> > > Plumbers about all the horrible bugs we've had lurking around in our
>> >> > > port despite it still getting to userspace and they suggested that I
>> >> > > enable CONFIG_PREEMPT in our defconfig as it'll help shake out more
>> >> > > issues.
>> >> > >
>> >> > > This patch enables CONFIG_PREEMPT in the single RISC-V defconfig.  It
>> >> > > still passes my tests (ie, booting Fedora on QEMU).  Maybe I'm too
>> >> > > paranoid, but I still don't trust our port enough to just pull the
>> >> > > trigger on this without at least accumulating some "Tested-by"s on it.
>> >> > >
>> >> > > Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
>> >> >
>> >> > I can only give you a
>> >> >
>> >> > Fails-miserably-for: Guenter Roeck <linux@roeck-us.net>
>> >> >
>> >> > Not the new defconfig itself, but the new defconfig plus a variety of
>> >> > selftest options. I don't know what exactly is failing, but here is
>> >> > my list of enabled selftests on top of defconfig:
>> >> >
>> >> > CONFIG_CRYPTO_MANAGER_DISABLE_TESTS=y
>> >> > CONFIG_CRC32_SELFTEST=y
>> >> > CONFIG_DEBUG_LOCKING_API_SELFTESTS=y
>> >> > CONFIG_DEBUG_NMI_SELFTEST=y
>> >> > CONFIG_DEBUG_RODATA_TEST=y
>> >> > CONFIG_DEBUG_TLBFLUSH=y
>> >> > CONFIG_DMATEST=y
>> >> > CONFIG_GLOB_SELFTEST=y
>> >> > CONFIG_OF_UNITTEST=y
>> >> > CONFIG_PCI_EPF_TEST=y
>> >> > CONFIG_PCI_ENDPOINT_TEST=y
>> >> > CONFIG_PROVE_LOCKING=y
>> >> > CONFIG_PROVE_RCU=y
>> >> > CONFIG_RCU_EQS_DEBUG=y
>> >> > CONFIG_STATIC_KEYS_SELFTEST=y
>> >> > CONFIG_STRING_SELFTEST=y
>> >> > CONFIG_TEST_BITMAP=y
>> >> > CONFIG_TEST_FIRMWARE=y
>> >> > CONFIG_TEST_SORT=y
>> >> > CONFIG_TEST_SYSCTL=y
>> >> > CONFIG_TEST_UUID=y
>> >> > CONFIG_USB_TEST=y
>> >> > CONFIG_USB_EHSET_TEST_FIXTURE=y
>> >> > CONFIG_USB_LINK_LAYER_TEST=y
>> >> > CONFIG_WW_MUTEX_SELFTEST=y
>> >> > CONFIG_TORTURE_TEST=y
>> >> > CONFIG_LOCK_TORTURE_TEST=y
>> >> > CONFIG_RCU_TORTURE_TEST=y
>> >> > CONFIG_RBTREE_TEST=y
>> >> > CONFIG_INTERVAL_TREE_TEST=y
>> >> >
>> >>
>> >> Update: defconfig+CONFIG_LOCK_TORTURE_TEST=y causes the hang
>> >> if CONFIG_PREEMPT=y.
>> >>
>> >
>> > Another update. CONFIG_RCU_TORTURE_TEST=y or CONFIG_WW_MUTEX_SELFTEST=y
>> > also result in hangs, only a bit later. I have now disabled all three test
>> > options in my riscv boot tests if CONFIG_PREEMPT=y. The lack of error
>> > reports in the future does _not_ mean that the problem has magically
>> > disappeared. I just find it pointless to keep testing a known broken
>> > configuration, even more so since doing so would hide other potential
>> > problems.
>>
>> Thanks.  I agree it's pointless to test more, as there appear to be lots of
>> bugs to fix already and this will just mask other bugs.
>>
>
> Last week, I encountered some locking issues in the kernel, so I tried
> to test the
> kernel with some relative selftests. Since I had already set CONFIG_PREEMPT=y,
> I encountered the same results in RCU_TORTURE_TEST and
> LOCK_TORTURE_TEST. I tried to debug it and found the hang was due to
> the lack of _TIF_NEED_RESCHED check for kernel threads in entry.S. I will send a
> patch to solve this problem and I hope you can give me some comments
> if you find some
> mistakes.

Thanks!

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