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

From: Palmer Dabbelt <palmer@sifive.com>
To: linux@roeck-us.net
Cc: linux-riscv@lists.infradead.org, aou@eecs.berkeley.edu
Subject: Re: [PATCH] RISC-V: Add CONFIG_PREEMPT=y to defconfig
Date: Wed, 26 Dec 2018 09:19:12 -0800 (PST)	[thread overview]
Message-ID: <mhng-856d9dbc-a4f1-47c3-a71c-d1f7ae82184b@palmer-si-x1c4> (raw)
In-Reply-To: <20181226032350.GA27044@roeck-us.net>

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.

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