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Date: Mon, 14 Nov 2022 11:24:17 -0500 From: Jason Baron <jbaron@...mai.com> To: Dmitry Safonov <dima@...sta.com>, linux-kernel@...r.kernel.org, David Ahern <dsahern@...nel.org>, Eric Dumazet <edumazet@...gle.com> Cc: Bob Gilligan <gilligan@...sta.com>, "David S. Miller" <davem@...emloft.net>, Dmitry Safonov <0x7f454c46@...il.com>, Francesco Ruggeri <fruggeri@...sta.com>, Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Salam Noureddine <noureddine@...sta.com>, netdev@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>, Josh Poimboeuf <jpoimboe@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Steven Rostedt <rostedt@...dmis.org> Subject: Re: [PATCH v3 1/3] jump_label: Prevent key->enabled int overflow On 11/11/22 16:23, Dmitry Safonov wrote: > diff --git a/kernel/jump_label.c b/kernel/jump_label.c > index 714ac4c3b556..f2c1aa351d41 100644 > --- a/kernel/jump_label.c > +++ b/kernel/jump_label.c > @@ -113,11 +113,38 @@ int static_key_count(struct static_key *key) > } > EXPORT_SYMBOL_GPL(static_key_count); > > -void static_key_slow_inc_cpuslocked(struct static_key *key) > +/*** > + * static_key_fast_inc - adds a user for a static key > + * @key: static key that must be already enabled > + * > + * The caller must make sure that the static key can't get disabled while > + * in this function. It doesn't patch jump labels, only adds a user to > + * an already enabled static key. > + * > + * Returns true if the increment was done. > + */ > +bool static_key_fast_inc(struct static_key *key) > { > int v, v1; > > STATIC_KEY_CHECK_USE(key); > + /* > + * Negative key->enabled has a special meaning: it sends > + * static_key_slow_inc() down the slow path, and it is non-zero > + * so it counts as "enabled" in jump_label_update(). Note that > + * atomic_inc_unless_negative() checks >= 0, so roll our own. > + */ > + for (v = atomic_read(&key->enabled); v > 0 && (v + 1) > 0; v = v1) { > + v1 = atomic_cmpxchg(&key->enabled, v, v + 1); > + if (likely(v1 == v)) > + return true; > + } > + return false; > +} > +EXPORT_SYMBOL_GPL(static_key_fast_inc); > + > +bool static_key_slow_inc_cpuslocked(struct static_key *key) > +{ > lockdep_assert_cpus_held(); > > /* > @@ -126,17 +153,9 @@ void static_key_slow_inc_cpuslocked(struct static_key *key) > * jump_label_update() process. At the same time, however, > * the jump_label_update() call below wants to see > * static_key_enabled(&key) for jumps to be updated properly. > - * > - * So give a special meaning to negative key->enabled: it sends > - * static_key_slow_inc() down the slow path, and it is non-zero > - * so it counts as "enabled" in jump_label_update(). Note that > - * atomic_inc_unless_negative() checks >= 0, so roll our own. > */ > - for (v = atomic_read(&key->enabled); v > 0; v = v1) { > - v1 = atomic_cmpxchg(&key->enabled, v, v + 1); > - if (likely(v1 == v)) > - return; > - } > + if (static_key_fast_inc(key)) > + return true; > > jump_label_lock(); > if (atomic_read(&key->enabled) == 0) { > @@ -148,16 +167,23 @@ void static_key_slow_inc_cpuslocked(struct static_key *key) > */ > atomic_set_release(&key->enabled, 1); > } else { > - atomic_inc(&key->enabled); > + if (WARN_ON_ONCE(static_key_fast_inc(key))) { Shouldn't that be negated to catch the overflow: if (WARN_ON_ONCE(!static_key_fast_inc(key))) > + jump_label_unlock(); > + return false; > + } > } > jump_label_unlock(); > + return true; > } > > -void static_key_slow_inc(struct static_key *key) > +bool static_key_slow_inc(struct static_key *key) > { > + bool ret; > + > cpus_read_lock(); > - static_key_slow_inc_cpuslocked(key); > + ret = static_key_slow_inc_cpuslocked(key); > cpus_read_unlock(); > + return ret; > } > EXPORT_SYMBOL_GPL(static_key_slow_inc); >
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