Re: [PATCH v5 bpf-next 2/3] bpf: introduce helper bpf_get_branch_snapshot
From: Peter Zijlstra <peterz@infradead.org>
Date: 2021-09-04 10:56:08
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lkml
Subsystem:
static branch/call, the rest · Maintainers:
Peter Zijlstra, Josh Poimboeuf, Jason Baron, Alice Ryhl, Linus Torvalds
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:quoted
quoted
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) {