Messages in this thread | | | Date | Wed, 15 Jun 2011 18:28:16 +0530 | From | Ankita Garg <> | Subject | Re: [PATCH] lkdtm: Fix race when crashpoint is hit multiple times before checking count |
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Hi,
On Tue, Jun 14, 2011 at 04:40:27PM -0700, Josh Hunt wrote: > We observed the crash point count going negative in cases where the crash point > is hit multiple times before the check of "count == 0" is done. Because of this > we never call lkdtm_do_action(). This patch just adds a spinlock to protect > count. >
Good catch! The fix Looks fine.
> Reported-by: Tapan Dhimant <tdhimant@akamai.com> > Signed-off-by: Josh Hunt <johunt@akamai.com>
Acked-by: Ankita Garg <ankita@in.ibm.com>
> --- > drivers/misc/lkdtm.c | 8 ++++++++ > 1 files changed, 8 insertions(+), 0 deletions(-) > > diff --git a/drivers/misc/lkdtm.c b/drivers/misc/lkdtm.c > index 81d7fa4..150cd70 100644 > --- a/drivers/misc/lkdtm.c > +++ b/drivers/misc/lkdtm.c > @@ -120,6 +120,7 @@ static int recur_count = REC_NUM_DEFAULT; > static enum cname cpoint = CN_INVALID; > static enum ctype cptype = CT_NONE; > static int count = DEFAULT_COUNT; > +static DEFINE_SPINLOCK(count_lock); > > module_param(recur_count, int, 0644); > MODULE_PARM_DESC(recur_count, " Recursion level for the stack overflow test, "\ > @@ -230,11 +231,14 @@ static const char *cp_name_to_str(enum cname name) > static int lkdtm_parse_commandline(void) > { > int i; > + unsigned long flags; > > if (cpoint_count < 1 || recur_count < 1) > return -EINVAL; > > + spin_lock_irqsave(&count_lock, flags); > count = cpoint_count; > + spin_unlock_irqrestore(&count_lock, flags); > > /* No special parameters */ > if (!cpoint_type && !cpoint_name) > @@ -349,6 +353,9 @@ static void lkdtm_do_action(enum ctype which) > > static void lkdtm_handler(void) > { > + unsigned long flags; > + > + spin_lock_irqsave(&count_lock, flags); > count--; > printk(KERN_INFO "lkdtm: Crash point %s of type %s hit, trigger in %d rounds\n", > cp_name_to_str(cpoint), cp_type_to_str(cptype), count); > @@ -357,6 +364,7 @@ static void lkdtm_handler(void) > lkdtm_do_action(cptype); > count = cpoint_count; > } > + spin_unlock_irqrestore(&count_lock, flags); > } > > static int lkdtm_register_cpoint(enum cname which)
-- Regards, Ankita Garg (ankita@in.ibm.com) Linux Technology Center IBM India Systems & Technology Labs, Bangalore, India
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