* Linus Torvalds <torva...@linux-foundation.org> wrote: > On Mon, Feb 27, 2017 at 11:57 PM, Ingo Molnar <mi...@kernel.org> wrote: > > > > Note that the uninlining allowed us to enable the underflow/overflow > > warnings > > unconditionally and remove the debug Kconfig switch: this might trigger new > > warnings in buggy code and turn crashes/use-after-free bugs into less > > harmful > > memory leaks. > > I'm ok with this, but that WARN() really needs to be a WARN_ON_ONCE(). > > Because once an underflow (or overflow) is happening, it tends to > _keep_ happening. And you may just have essentially DoS'ed the machine > that is now spending all its time writing those logs to disk. > > Yes, yes, quiet independently of this we should limit WARN printouts > (and do the reverse: turn a "once" to mean "once in a blue moon" > rather than actually just once), but particularly for this kind of > "never happens" thing, it really is better to just warn once.
Good point - I've done this in the attached patch. Thanks, Ingo =================> >From 9dcfe2c75b51f454f39c2de4756e841228865b47 Mon Sep 17 00:00:00 2001 From: Ingo Molnar <mi...@kernel.org> Date: Wed, 1 Mar 2017 09:25:55 +0100 Subject: [PATCH] locking/refcounts: Change WARN() to WARN_ONCE() Linus noticed that the new refcount.h APIs used WARN(), which would turn into a dmesg DoS if it triggers frequently on some buggy driver. So make sure we only warn once. These warnings are never supposed to happen, so it's typically not a problem to lose subsequent warnings. Suggested-by: Linus Torvalds <torva...@linux-foundation.org> Cc: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: Elena Reshetova <elena.reshet...@intel.com> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Link: http://lkml.kernel.org/r/CA+55aFzbYUTZ=oqz2ygdjy0c2_n6odhtfqj6v+m5xwmdxsu...@mail.gmail.com Signed-off-by: Ingo Molnar <mi...@kernel.org> --- lib/refcount.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/lib/refcount.c b/lib/refcount.c index 1d33366189d1..aa09ad3c30b0 100644 --- a/lib/refcount.c +++ b/lib/refcount.c @@ -58,7 +58,7 @@ bool refcount_add_not_zero(unsigned int i, refcount_t *r) val = old; } - WARN(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n"); + WARN_ONCE(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n"); return true; } @@ -66,7 +66,7 @@ EXPORT_SYMBOL_GPL(refcount_add_not_zero); void refcount_add(unsigned int i, refcount_t *r) { - WARN(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n"); + WARN_ONCE(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n"); } EXPORT_SYMBOL_GPL(refcount_add); @@ -97,7 +97,7 @@ bool refcount_inc_not_zero(refcount_t *r) val = old; } - WARN(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n"); + WARN_ONCE(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n"); return true; } @@ -111,7 +111,7 @@ EXPORT_SYMBOL_GPL(refcount_inc_not_zero); */ void refcount_inc(refcount_t *r) { - WARN(!refcount_inc_not_zero(r), "refcount_t: increment on 0; use-after-free.\n"); + WARN_ONCE(!refcount_inc_not_zero(r), "refcount_t: increment on 0; use-after-free.\n"); } EXPORT_SYMBOL_GPL(refcount_inc); @@ -125,7 +125,7 @@ bool refcount_sub_and_test(unsigned int i, refcount_t *r) new = val - i; if (new > val) { - WARN(new > val, "refcount_t: underflow; use-after-free.\n"); + WARN_ONCE(new > val, "refcount_t: underflow; use-after-free.\n"); return false; } @@ -164,7 +164,7 @@ EXPORT_SYMBOL_GPL(refcount_dec_and_test); void refcount_dec(refcount_t *r) { - WARN(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n"); + WARN_ONCE(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n"); } EXPORT_SYMBOL_GPL(refcount_dec); @@ -204,7 +204,7 @@ bool refcount_dec_not_one(refcount_t *r) new = val - 1; if (new > val) { - WARN(new > val, "refcount_t: underflow; use-after-free.\n"); + WARN_ONCE(new > val, "refcount_t: underflow; use-after-free.\n"); return true; }