Messages in this thread Patch in this message | | | Date | Wed, 6 May 2020 16:15:47 -0500 | From | Josh Poimboeuf <> | Subject | Re: [PATCH v4 16/18] static_call: Allow early init |
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On Fri, May 01, 2020 at 10:29:05PM +0200, Peter Zijlstra wrote: > In order to use static_call() to wire up x86_pmu, we need to > initialize earlier; copy some of the tricks from jump_label to enable > this. > > Primarily we overload key->next to store a sites pointer when there > are no modules, this avoids having to use kmalloc() to initialize the > sites and allows us to run much earlier. > > (arguably, this is much much earlier than needed for perf, but it > might allow other uses.) > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- > arch/x86/kernel/setup.c | 2 + > arch/x86/kernel/static_call.c | 8 +++++- > include/linux/static_call.h | 15 ++++++++++-- > kernel/static_call.c | 52 +++++++++++++++++++++++++++++++++++++++--- > 4 files changed, 71 insertions(+), 6 deletions(-)
This doesn't work when the key is defined in a module. In __static_call_update(), first.site_mod->mod is NULL, but static_call_key_sites() points to the module's call sites.
This seems to fix it (sorry, also has the 'next' -> 'mods' rename). The actual fix is in static_call_key_sites() and static_call_key_mods().
diff --git a/include/linux/static_call.h b/include/linux/static_call.h index e112553cfce6..ee55075707f1 100644 --- a/include/linux/static_call.h +++ b/include/linux/static_call.h @@ -110,9 +110,10 @@ struct static_call_mod { struct static_call_key { void *func; union { - /* bit0 => 0 - next, 1 - sites */ + /* bit 0: 0 = mods; 1 = sites */ unsigned long type; - struct static_call_mod *next; + + struct static_call_mod *mods; struct static_call_site *sites; }; }; diff --git a/kernel/static_call.c b/kernel/static_call.c index 783953db28c4..d78e50c5b8a3 100644 --- a/kernel/static_call.c +++ b/kernel/static_call.c @@ -94,23 +94,23 @@ static inline void static_call_sort_entries(struct static_call_site *start, static_call_site_cmp, static_call_site_swap); } -static inline bool static_call_key_has_next(struct static_call_key *key) +static inline bool static_call_key_has_mods(struct static_call_key *key) { return !(key->type & 1); } -static inline struct static_call_mod *static_call_key_next(struct static_call_key *key) +static inline struct static_call_mod *static_call_key_mods(struct static_call_key *key) { - if (static_call_key_has_next(key)) - return key->next->next; + if (!static_call_key_has_mods(key)) + return NULL; - return NULL; + return key->mods; } static inline struct static_call_site *static_call_key_sites(struct static_call_key *key) { - if (static_call_key_has_next(key)) - return key->next->sites; + if (static_call_key_has_mods(key)) + return NULL; return (struct static_call_site *)(key->type & ~1); } @@ -118,7 +118,12 @@ static inline struct static_call_site *static_call_key_sites(struct static_call_ void __static_call_update(struct static_call_key *key, void *tramp, void *func) { struct static_call_site *site, *stop; - struct static_call_mod *site_mod, first; + struct static_call_mod *site_mod; + struct static_call_mod first = { + .next = static_call_key_mods(key), + .mod = NULL, + .sites = static_call_key_sites(key), + }; cpus_read_lock(); static_call_lock(); @@ -137,17 +142,14 @@ void __static_call_update(struct static_call_key *key, void *tramp, void *func) if (WARN_ON_ONCE(!static_call_initialized)) goto done; - first = (struct static_call_mod){ - .next = static_call_key_next(key), - .mod = NULL, - .sites = static_call_key_sites(key), - }; - for (site_mod = &first; site_mod; site_mod = site_mod->next) { if (!site_mod->sites) { /* * This can happen if the static call key is defined in * a module which doesn't use it. + * + * It also happens in the has_mods case, where the + * 'first' entry has no sites associated with it. */ continue; } @@ -228,12 +230,12 @@ static int __static_call_init(struct module *mod, if (!site_mod) return -ENOMEM; - if (!static_call_key_has_next(key)) { + if (!static_call_key_has_mods(key)) { site_mod->mod = NULL; site_mod->next = NULL; site_mod->sites = static_call_key_sites(key); - key->next = site_mod; + key->mods = site_mod; site_mod = kzalloc(sizeof(*site_mod), GFP_KERNEL); if (!site_mod) @@ -242,8 +244,8 @@ static int __static_call_init(struct module *mod, site_mod->mod = mod; site_mod->sites = site; - site_mod->next = key->next; - key->next = site_mod; + site_mod->next = key->mods; + key->mods = site_mod; } do_transform: @@ -328,7 +330,7 @@ static void static_call_del_module(struct module *mod) prev_key = key; - for (prev = &key->next, site_mod = key->next; + for (prev = &key->mods, site_mod = key->mods; site_mod && site_mod->mod != mod; prev = &site_mod->next, site_mod = site_mod->next) ;
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