linux-kernel - Re: 2.6.25-rc7: Ugh.

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Date:	Fri, 28 Mar 2008 01:46:46 -0400
From:	Mark Lord <lkml@....ca>
To:	David Miller <davem@...emloft.net>
Cc:	jkosina@...e.cz, gregkh@...e.de, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org, pavel@...e.cz, akpm@...ux-foundation.org
Subject: Re: 2.6.25-rc7: Ugh.

David Miller wrote:
> From: Mark Lord <lkml@....ca>
> Date: Thu, 27 Mar 2008 21:57:55 -0400
> 
>> I don't have the XX days necessary for git-bisect right now.
> 
> I wish people would say stuff like this.
..

I just did, thanks.

In this case, a bisect would be a complete waste of time,
because whatever is wrong seems to be a timing-related race
condition of some kind.

Merely rebuilding the kernel with slightly different debug flags
affects things, so trying to bisect it would be a super waste of
time in all probability.

When I rebuilt with all debug stuff on, the kernel was worse than
before, and just gave the "black screen of nothing" on resume,
with a hung system.

At least before the system didn't hang.

Now I've just booted with a differently configured kernel,
with only about half of the debug flags turned on.
This one resumes from suspend, and *with* working USB too.

Ugh. Gotta love it when the bug is so subtle that turning on
the debug flags makes it (1) get worse, and/or (2) get cured.

Here's the abbreviated diff between broken (no USB on resume, no hang),
and working (good USB, no hang) .config files.

--- dot_config.nousb	2008-03-27 22:43:50.000000000 -0400
+++ dot_config.works	2008-03-28 01:29:22.000000000 -0400
-CONFIG_LOG_BUF_SHIFT=16
+CONFIG_LOG_BUF_SHIFT=17
-# CONFIG_KALLSYMS_ALL is not set
+CONFIG_KALLSYMS_ALL=y
-# CONFIG_MAC80211_DEBUGFS is not set
-# CONFIG_RTC is not set
-CONFIG_GEN_RTC=y
-CONFIG_GEN_RTC_X=y
+CONFIG_RTC=y
+CONFIG_SND_RTCTIMER=m
+CONFIG_SND_SEQ_RTCTIMER_DEFAULT=y
-CONFIG_RTC_LIB=y
-CONFIG_RTC_CLASS=y
-
-#
-# Conflicting RTC option has been selected, check GEN_RTC and RTC
-#
-CONFIG_RTC_HCTOSYS=y
-CONFIG_RTC_HCTOSYS_DEVICE="rtc0"
-# CONFIG_RTC_DEBUG is not set
-
-#
-# RTC interfaces
-#
-CONFIG_RTC_INTF_SYSFS=y
-CONFIG_RTC_INTF_PROC=y
-CONFIG_RTC_INTF_DEV=y
-# CONFIG_RTC_INTF_DEV_UIE_EMUL is not set
-CONFIG_RTC_DRV_TEST=m
-
-#
-# I2C RTC drivers
-#
-CONFIG_RTC_DRV_DS1307=m
-CONFIG_RTC_DRV_DS1374=m
-CONFIG_RTC_DRV_DS1672=m
-CONFIG_RTC_DRV_MAX6900=m
-CONFIG_RTC_DRV_RS5C372=m
-CONFIG_RTC_DRV_ISL1208=m
-CONFIG_RTC_DRV_X1205=m
-CONFIG_RTC_DRV_PCF8563=m
-CONFIG_RTC_DRV_PCF8583=m
-# CONFIG_RTC_DRV_M41T80 is not set
-# CONFIG_RTC_DRV_S35390A is not set
-
-#
-# SPI RTC drivers
-#
-
-#
-# Platform RTC drivers
-#
-CONFIG_RTC_DRV_CMOS=y
-CONFIG_RTC_DRV_DS1511=m
-CONFIG_RTC_DRV_DS1553=m
-CONFIG_RTC_DRV_DS1742=m
-# CONFIG_RTC_DRV_STK17TA8 is not set
-CONFIG_RTC_DRV_M48T86=m
-# CONFIG_RTC_DRV_M48T59 is not set
-CONFIG_RTC_DRV_V3020=m
-
-#
-# on-CPU RTC drivers
-#
+# CONFIG_RTC_CLASS is not set
-# CONFIG_JBD_DEBUG is not set
-CONFIG_DLM=m
-# CONFIG_DLM_DEBUG is not set
+# CONFIG_DLM is not set
-CONFIG_DEBUG_FS=y
+# CONFIG_DEBUG_FS is not set
-CONFIG_TIMER_STATS=y
-# CONFIG_DEBUG_SLAB is not set
+# CONFIG_TIMER_STATS is not set
+CONFIG_DEBUG_SLAB=y
+CONFIG_DEBUG_SLAB_LEAK=y
-# CONFIG_DEBUG_SPINLOCK is not set
-# CONFIG_DEBUG_MUTEXES is not set
-# CONFIG_DEBUG_LOCK_ALLOC is not set
-# CONFIG_PROVE_LOCKING is not set
+CONFIG_DEBUG_SPINLOCK=y
+CONFIG_DEBUG_MUTEXES=y
+CONFIG_DEBUG_LOCK_ALLOC=y
+CONFIG_PROVE_LOCKING=y
+CONFIG_LOCKDEP=y
 # CONFIG_LOCK_STAT is not set
-# CONFIG_DEBUG_SPINLOCK_SLEEP is not set
-# CONFIG_DEBUG_LOCKING_API_SELFTESTS is not set
-# CONFIG_DEBUG_KOBJECT is not set
-# CONFIG_DEBUG_HIGHMEM is not set
+CONFIG_DEBUG_LOCKDEP=y
+CONFIG_TRACE_IRQFLAGS=y
+CONFIG_DEBUG_SPINLOCK_SLEEP=y
+CONFIG_DEBUG_LOCKING_API_SELFTESTS=y
+CONFIG_STACKTRACE=y
+CONFIG_DEBUG_KOBJECT=y
+CONFIG_DEBUG_HIGHMEM=y
-# CONFIG_DEBUG_INFO is not set
-# CONFIG_DEBUG_VM is not set
-# CONFIG_DEBUG_LIST is not set
+CONFIG_DEBUG_INFO=y
+CONFIG_DEBUG_VM=y
+CONFIG_DEBUG_LIST=y
-# CONFIG_FRAME_POINTER is not set
+CONFIG_FRAME_POINTER=y
-# CONFIG_DEBUG_STACKOVERFLOW is not set
-# CONFIG_DEBUG_STACK_USAGE is not set
+CONFIG_DEBUG_STACKOVERFLOW=y
+CONFIG_DEBUG_STACK_USAGE=y
-CONFIG_4KSTACKS=y
+# CONFIG_4KSTACKS is not set
-# CONFIG_DEBUG_BOOT_PARAMS is not set
--
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