Messages in this thread Patch in this message | | | Date | Wed, 1 Mar 2017 09:30:00 +0100 | From | Ingo Molnar <> | Subject | [PATCH] locking/refcounts: Change WARN() to WARN_ONCE() |
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* Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Mon, Feb 27, 2017 at 11:57 PM, Ingo Molnar <mingo@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 <mingo@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 <torvalds@linux-foundation.org> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Elena Reshetova <elena.reshetova@intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/CA+55aFzbYUTZ=oqZ2YgDjY0C2_n6ODhTfqj6V+m5xWmDxsuB0w@mail.gmail.com Signed-off-by: Ingo Molnar <mingo@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; }
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