Messages in this thread Patch in this message | | | Date | Wed, 24 Sep 2008 10:36:09 +0100 | From | Frédéric Weisbecker <> | Subject | Re: [Patch -tip 0/4] Creation of the initcall tracer |
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Ingo Molnar a écrit : > * Ingo Molnar <mingo@elte.hu> wrote: > >> i've integrated tip/tracing/fastboot into tip/master and have started >> testing it. It passed the basic tests already so i've just pushed out >> the new tip/master. Please double-check that i have not messed up the >> rename or the integration somewhere. > > FYI, -tip testing found a boot hang with CONFIG_BOOT_TRACER=y, on a > 32-bit T60 laptop. I've attached the config that provokes the hang. (you > need initcall_debug on the boot commandline) > > The hang always happens after a specific initcall, shortly after tracing > is enabled. It just hangs indefinitely there, the last line displayed > was: > > [ 0.004017] initcall ehci_hcd_init+0x0/0x80 returned 0 after 228 msecs > > it should have printed this next: > > [ 0.808024] calling ohci_hcd_mod_init+0x0/0x80 @ 10 > > but that line is never printed. > > i've bisected the hang down to this specific commit: > > | 35df98dfe2b2503436a8cfda301657810df50a3a is first bad commit > | commit 35df98dfe2b2503436a8cfda301657810df50a3a > | Author: Frédéric Weisbecker <fweisbec@gmail.com> > | Date: Tue Sep 23 11:38:18 2008 +0100 > | > | tracing/ftrace: launch boot tracing after pre-smp initcalls > > An idea: maybe the boot tracer is interacting with the ftrace self-tests > somehow? CONFIG_FTRACE_SELFTEST=y is enabled. > > another thing i noticed is that the sysprof tracer was initialized and > self-tested shortly before the hang occured. Might be unrelated. > > the bisection log is: > > # bad: [6522eab5] Merge branch 'x86/uv' > # good: [699b81f5] Merge branch 'x86/iommu' > # bad: [8007aae9] timers: fix build error in !oneshot case > # good: [7f29b23d] Merge branch 'core/rcu' > # bad: [a54f17e3] manual merge of tracing/fastboot > # good: [bcbbe946] tracing/ftrace: make tracing suitable to run the b > # good: [d7095e5a] Merge branch 'fastboot' > # bad: [35df98df] tracing/ftrace: launch boot tracing after pre-smp > # good: [42aaa6be] tracing/ftrace: give an entry on the config for bo > > Ingo > Ingo Molnar a écrit : > * Ingo Molnar <mingo@elte.hu> wrote: > >> i've integrated tip/tracing/fastboot into tip/master and have started >> testing it. It passed the basic tests already so i've just pushed out >> the new tip/master. Please double-check that i have not messed up the >> rename or the integration somewhere. > > FYI, -tip testing found a boot hang with CONFIG_BOOT_TRACER=y, on a > 32-bit T60 laptop. I've attached the config that provokes the hang. (you > need initcall_debug on the boot commandline) > > The hang always happens after a specific initcall, shortly after tracing > is enabled. It just hangs indefinitely there, the last line displayed > was: > > [ 0.004017] initcall ehci_hcd_init+0x0/0x80 returned 0 after 228 msecs > > it should have printed this next: > > [ 0.808024] calling ohci_hcd_mod_init+0x0/0x80 @ 10 > > but that line is never printed. > > i've bisected the hang down to this specific commit: > > | 35df98dfe2b2503436a8cfda301657810df50a3a is first bad commit > | commit 35df98dfe2b2503436a8cfda301657810df50a3a > | Author: Frédéric Weisbecker <fweisbec@gmail.com> > | Date: Tue Sep 23 11:38:18 2008 +0100 > | > | tracing/ftrace: launch boot tracing after pre-smp initcalls > > An idea: maybe the boot tracer is interacting with the ftrace self-tests > somehow? CONFIG_FTRACE_SELFTEST=y is enabled. > > another thing i noticed is that the sysprof tracer was initialized and > self-tested shortly before the hang occured. Might be unrelated. > > the bisection log is: > > # bad: [6522eab5] Merge branch 'x86/uv' > # good: [699b81f5] Merge branch 'x86/iommu' > # bad: [8007aae9] timers: fix build error in !oneshot case > # good: [7f29b23d] Merge branch 'core/rcu' > # bad: [a54f17e3] manual merge of tracing/fastboot > # good: [bcbbe946] tracing/ftrace: make tracing suitable to run the b > # good: [d7095e5a] Merge branch 'fastboot' > # bad: [35df98df] tracing/ftrace: launch boot tracing after pre-smp > # good: [42aaa6be] tracing/ftrace: give an entry on the config for bo > > Ingo >
Hehe! I was preparing a patch because I saw last night that the self-tests were reseting and touching the ring-buffer during the initcall tracing. And now I can see the results of this problem....
Following is a patch that should fix it. Thanks for this report! --- [Patch -tip] Disable tracers self-tests when boot tracer is selected
The tracing engine resets the ring buffer and the tracers touch it too during self-tests. These self-tests happen during tracers registering and work against boot tracing which is logging initcalls. We have to disable tracing self-tests if the boot-tracer is selected.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Reported-by: Ingo Molnar <mingo@elte.hu> --- diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index 81a17ef..87c9282 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -126,7 +126,9 @@ config BOOT_TRACER the timings of the initcalls. Its aim is to be parsed by the /scripts/bootgraph.pl tool to produce pretty graphics about boot inefficiencies, giving a visual representation of the - delays during initcalls. + delays during initcalls. Note that tracers self tests can't + be enabled if this tracer is selected since only one tracer + should touch the tracing buffer at a time. config STACK_TRACER bool "Trace max stack" @@ -168,8 +170,7 @@ config FTRACE_SELFTEST config FTRACE_STARTUP_TEST bool "Perform a startup test on ftrace" - depends on TRACING - depends on DEBUG_KERNEL + depends on TRACING && DEBUG_KERNEL && !BOOT_TRACER select FTRACE_SELFTEST help This option performs a series of startup tests on ftrace. On bootup | |