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Date: Thu, 28 Apr 2022 09:01:13 +0800 From: Xiaoming Ni <nixiaoming@...wei.com> To: "Guilherme G. Piccoli" <gpiccoli@...lia.com>, <akpm@...ux-foundation.org>, <bhe@...hat.com>, <pmladek@...e.com>, <kexec@...ts.infradead.org> CC: <linux-kernel@...r.kernel.org>, <bcm-kernel-feedback-list@...adcom.com>, <coresight@...ts.linaro.org>, <linuxppc-dev@...ts.ozlabs.org>, <linux-alpha@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>, <linux-edac@...r.kernel.org>, <linux-hyperv@...r.kernel.org>, <linux-leds@...r.kernel.org>, <linux-mips@...r.kernel.org>, <linux-parisc@...r.kernel.org>, <linux-pm@...r.kernel.org>, <linux-remoteproc@...r.kernel.org>, <linux-s390@...r.kernel.org>, <linux-tegra@...r.kernel.org>, <linux-um@...ts.infradead.org>, <linux-xtensa@...ux-xtensa.org>, <netdev@...r.kernel.org>, <openipmi-developer@...ts.sourceforge.net>, <rcu@...r.kernel.org>, <sparclinux@...r.kernel.org>, <xen-devel@...ts.xenproject.org>, <x86@...nel.org>, <kernel-dev@...lia.com>, <kernel@...ccoli.net>, <halves@...onical.com>, <fabiomirmar@...il.com>, <alejandro.j.jimenez@...cle.com>, <andriy.shevchenko@...ux.intel.com>, <arnd@...db.de>, <bp@...en8.de>, <corbet@....net>, <d.hatayama@...fujitsu.com>, <dave.hansen@...ux.intel.com>, <dyoung@...hat.com>, <feng.tang@...el.com>, <gregkh@...uxfoundation.org>, <mikelley@...rosoft.com>, <hidehiro.kawai.ez@...achi.com>, <jgross@...e.com>, <john.ogness@...utronix.de>, <keescook@...omium.org>, <luto@...nel.org>, <mhiramat@...nel.org>, <mingo@...hat.com>, <paulmck@...nel.org>, <peterz@...radead.org>, <rostedt@...dmis.org>, <senozhatsky@...omium.org>, <stern@...land.harvard.edu>, <tglx@...utronix.de>, <vgoyal@...hat.com>, <vkuznets@...hat.com>, <will@...nel.org>, Arjan van de Ven <arjan@...ux.intel.com>, Cong Wang <xiyou.wangcong@...il.com>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Valentin Schneider <valentin.schneider@....com> Subject: Re: [PATCH 18/30] notifier: Show function names on notifier routines if DEBUG_NOTIFIERS is set On 2022/4/28 6:49, Guilherme G. Piccoli wrote: > Currently we have a debug infrastructure in the notifiers file, but > it's very simple/limited. This patch extends it by: > > (a) Showing all registered/unregistered notifiers' callback names; > > (b) Adding a dynamic debug tuning to allow showing called notifiers' > function names. Notice that this should be guarded as a tunable since > it can flood the kernel log buffer. > > Cc: Arjan van de Ven <arjan@...ux.intel.com> > Cc: Cong Wang <xiyou.wangcong@...il.com> > Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de> > Cc: Valentin Schneider <valentin.schneider@....com> > Cc: Xiaoming Ni <nixiaoming@...wei.com> > Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com> > --- > > We have some design decisions that worth discussing here: > > (a) First of call, using C99 helps a lot to write clear and concise code, but > due to commit 4d94f910e79a ("Kbuild: use -Wdeclaration-after-statement") we > have a warning if mixing variable declarations with code. For this patch though, > doing that makes the code way clear, so decision was to add the debug code > inside brackets whenever this warning pops up. We can change that, but that'll > cause more ifdefs in the same function. > > (b) In the symbol lookup helper function, we modify the parameter passed but > even more, we return it as well! This is unusual and seems unnecessary, but was > the strategy taken to allow embedding such function in the pr_debug() call. > > Not doing that would likely requiring 3 symbol_name variables to avoid > concurrency (registering notifier A while calling notifier B) - we rely in > local variables as a serialization mechanism. > > We're open for suggestions in case this design is not appropriate; > thanks in advance! > > kernel/notifier.c | 48 +++++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 46 insertions(+), 2 deletions(-) > > diff --git a/kernel/notifier.c b/kernel/notifier.c > index ba005ebf4730..21032ebcde57 100644 > --- a/kernel/notifier.c > +++ b/kernel/notifier.c > @@ -7,6 +7,22 @@ > #include <linux/vmalloc.h> > #include <linux/reboot.h> > > +#ifdef CONFIG_DEBUG_NOTIFIERS > +#include <linux/kallsyms.h> > + > +/* > + * Helper to get symbol names in case DEBUG_NOTIFIERS is set. > + * Return the modified parameter is a strategy used to achieve > + * the pr_debug() functionality - with this, function is only > + * executed if the dynamic debug tuning is effectively set. > + */ > +static inline char *notifier_name(struct notifier_block *nb, char *sym_name) > +{ > + lookup_symbol_name((unsigned long)(nb->notifier_call), sym_name); > + return sym_name; > +} > +#endif > + > /* > * Notifier list for kernel code which wants to be called > * at shutdown. This is used to stop any idling DMA operations > @@ -34,20 +50,41 @@ static int notifier_chain_register(struct notifier_block **nl, > } > n->next = *nl; > rcu_assign_pointer(*nl, n); > + > +#ifdef CONFIG_DEBUG_NOTIFIERS > + { > + char sym_name[KSYM_NAME_LEN]; > + > + pr_info("notifiers: registered %s()\n", > + notifier_name(n, sym_name)); > + } Duplicate Code. Is it better to use __func__ and %pS? pr_info("%s: %pS\n", __func__, n->notifier_call); > +#endif > return 0; > } > > static int notifier_chain_unregister(struct notifier_block **nl, > struct notifier_block *n) > { > + int ret = -ENOENT; > + > while ((*nl) != NULL) { > if ((*nl) == n) { > rcu_assign_pointer(*nl, n->next); > - return 0; > + ret = 0; > + break; > } > nl = &((*nl)->next); > } > - return -ENOENT; > + > +#ifdef CONFIG_DEBUG_NOTIFIERS > + if (!ret) { > + char sym_name[KSYM_NAME_LEN]; > + > + pr_info("notifiers: unregistered %s()\n", > + notifier_name(n, sym_name)); > + } Duplicate Code. Is it better to use __func__ and %pS? pr_info("%s: %pS\n", __func__, n->notifier_call); > +#endif > + return ret; > } > > /** > @@ -80,6 +117,13 @@ static int notifier_call_chain(struct notifier_block **nl, > nb = next_nb; > continue; > } > + Is the "#ifdef" missing here? > + { > + char sym_name[KSYM_NAME_LEN]; > + > + pr_debug("notifiers: calling %s()\n", > + notifier_name(nb, sym_name)); Duplicate Code. Is it better to use __func__ and %pS? pr_info("%s: %pS\n", __func__, n->notifier_call); > + } > #endif > ret = nb->notifier_call(nb, val, v); > > Thanks Xiaoming Ni
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