From: Peter Zijlstra <peterz@infradead.org> To: Andrii Nakryiko <andrii.nakryiko@gmail.com> Cc: Song Liu <songliubraving@fb.com>, bpf <bpf@vger.kernel.org>, open list <linux-kernel@vger.kernel.org>, Arnaldo Carvalho de Melo <acme@kernel.org>, Ingo Molnar <mingo@redhat.com>, Kajol Jain <kjain@linux.ibm.com>, Kernel Team <kernel-team@fb.com> Subject: Re: [PATCH v5 bpf-next 2/3] bpf: introduce helper bpf_get_branch_snapshot Date: Sat, 4 Sep 2021 12:55:29 +0200 [thread overview] Message-ID: <20210904105529.GA5106@worktop.programming.kicks-ass.net> (raw) In-Reply-To: <20210904102430.GD4323@worktop.programming.kicks-ass.net> On Sat, Sep 04, 2021 at 12:24:30PM +0200, Peter Zijlstra wrote: > On Fri, Sep 03, 2021 at 10:10:16AM -0700, Andrii Nakryiko wrote: > > > I suppose you have to have this helper function because the JIT cannot > > > emit static_call()... although in this case one could cheat and simply > > > emit a call to static_call_query() and not bother with dynamic updates > > > (because there aren't any). > > > > If that's safe, let's do it. > > I'll try and remember to look into static_call_lock(), a means of > forever denying future static_call_update() calls. That should make this > more obvious. A little something like so I suppose.... we don't really have spare bits in the !INLINE case :/ --- diff --git a/include/linux/static_call.h b/include/linux/static_call.h index 3e56a9751c06..b0feccd56d37 100644 --- a/include/linux/static_call.h +++ b/include/linux/static_call.h @@ -174,6 +174,10 @@ struct static_call_tramp_key { s32 key; }; +extern void __static_call_lock(struct static_call_key *key); + +#define static_call_lock(name) __static_call_lock(&STATIC_CALL_KEY(name)) + extern void __static_call_update(struct static_call_key *key, void *tramp, void *func); extern int static_call_mod_init(struct module *mod); extern int static_call_text_reserved(void *start, void *end); @@ -215,6 +219,8 @@ extern long __static_call_return0(void); #elif defined(CONFIG_HAVE_STATIC_CALL) +#define static_call_lock(name) + static inline int static_call_init(void) { return 0; } #define __DEFINE_STATIC_CALL(name, _func, _func_init) \ @@ -268,6 +274,8 @@ static inline long __static_call_return0(void) #else /* Generic implementation */ +#define static_call_lock(name) + static inline int static_call_init(void) { return 0; } static inline long __static_call_return0(void) diff --git a/include/linux/static_call_types.h b/include/linux/static_call_types.h index 5a00b8b2cf9f..e40a3b595c4a 100644 --- a/include/linux/static_call_types.h +++ b/include/linux/static_call_types.h @@ -62,6 +62,7 @@ struct static_call_key { void *func; union { /* bit 0: 0 = mods, 1 = sites */ + /* but 1: locked */ unsigned long type; struct static_call_mod *mods; struct static_call_site *sites; diff --git a/kernel/static_call.c b/kernel/static_call.c index 43ba0b1e0edb..a1ba93fbad29 100644 --- a/kernel/static_call.c +++ b/kernel/static_call.c @@ -104,6 +104,11 @@ static inline bool static_call_key_has_mods(struct static_call_key *key) return !(key->type & 1); } +static inline bool static_call_key_is_locked(struct static_call_key *key) +{ + return !!(key->type & 2); +} + static inline struct static_call_mod *static_call_key_next(struct static_call_key *key) { if (!static_call_key_has_mods(key)) @@ -117,7 +122,7 @@ static inline struct static_call_site *static_call_key_sites(struct static_call_ if (static_call_key_has_mods(key)) return NULL; - return (struct static_call_site *)(key->type & ~1); + return (struct static_call_site *)(key->type & ~3); } void __static_call_update(struct static_call_key *key, void *tramp, void *func) @@ -125,6 +130,9 @@ 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; + if (WARN_ON_ONCE(static_call_key_is_locked(key))) + return; + cpus_read_lock(); static_call_lock(); @@ -418,6 +426,18 @@ static void static_call_del_module(struct module *mod) } } +void __static_call_lock(struct static_call_key *key) +{ + cpus_read_lock(); + static_call_lock(); + + WARN_ON_ONCE(static_call_key_is_locked(key)); + key->type |= 2; + + static_call_unlock(); + cpus_read_unlock(); +} + static int static_call_module_notify(struct notifier_block *nb, unsigned long val, void *data) {
next prev parent reply other threads:[~2021-09-04 10:56 UTC|newest] Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-09-02 16:57 [PATCH v5 bpf-next 0/3] bpf: introduce bpf_get_branch_snapshot Song Liu 2021-09-02 16:57 ` [PATCH v5 bpf-next 1/3] perf: enable branch record for software events Song Liu 2021-09-02 20:49 ` John Fastabend 2021-09-03 8:02 ` Peter Zijlstra 2021-09-03 16:50 ` Song Liu 2021-09-07 18:59 ` Song Liu 2021-09-07 20:50 ` Andrii Nakryiko 2021-09-03 8:27 ` Peter Zijlstra 2021-09-03 16:45 ` Song Liu 2021-09-04 10:18 ` Peter Zijlstra 2021-09-02 16:57 ` [PATCH v5 bpf-next 2/3] bpf: introduce helper bpf_get_branch_snapshot Song Liu 2021-09-02 20:56 ` John Fastabend 2021-09-02 22:04 ` Song Liu 2021-09-02 22:53 ` Andrii Nakryiko 2021-09-02 23:03 ` Song Liu 2021-09-02 23:05 ` Andrii Nakryiko 2021-09-03 1:03 ` Alexei Starovoitov 2021-09-03 8:28 ` Peter Zijlstra 2021-09-03 16:58 ` Song Liu 2021-09-03 8:47 ` Peter Zijlstra 2021-09-03 17:06 ` Song Liu 2021-09-03 17:10 ` Andrii Nakryiko 2021-09-04 10:24 ` Peter Zijlstra 2021-09-04 10:55 ` Peter Zijlstra [this message] 2021-09-02 16:57 ` [PATCH v5 bpf-next 3/3] selftests/bpf: add test for bpf_get_branch_snapshot Song Liu 2021-09-02 21:05 ` John Fastabend 2021-09-02 22:54 ` [PATCH v5 bpf-next 0/3] bpf: introduce bpf_get_branch_snapshot Andrii Nakryiko
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