From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Kelley (LINUX) Date: Fri, 29 Apr 2022 16:27:42 +0000 Subject: [PATCH 18/30] notifier: Show function names on notifier routines if DEBUG_NOTIFIERS is set In-Reply-To: <20220427224924.592546-19-gpiccoli@igalia.com> References: <20220427224924.592546-1-gpiccoli@igalia.com> <20220427224924.592546-19-gpiccoli@igalia.com> Message-ID: List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: kexec@lists.infradead.org From: Guilherme G. Piccoli Sent: Wednesday, April 27, 2022 3:49 PM > > 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 > Cc: Cong Wang > Cc: Sebastian Andrzej Siewior > Cc: Valentin Schneider > Cc: Xiaoming Ni > Signed-off-by: Guilherme G. Piccoli > --- > > 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 s/call/all/ > 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 > #include > > +#ifdef CONFIG_DEBUG_NOTIFIERS > +#include > + > +/* > + * 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)); > + } > +#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)); > + } > +#endif > + return ret; > } > > /** > @@ -80,6 +117,13 @@ static int notifier_call_chain(struct notifier_block **nl, > nb = next_nb; > continue; > } > + > + { > + char sym_name[KSYM_NAME_LEN]; > + > + pr_debug("notifiers: calling %s()\n", > + notifier_name(nb, sym_name)); > + } > #endif > ret = nb->notifier_call(nb, val, v); > > -- > 2.36.0