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Add a new kernel option, MALLOC_MAKE_FAILURES, which compiles

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in a debugging feature causing M_NOWAIT allocations to fail at
a specified rate.  This can be useful for detecting poor
handling of M_NOWAIT: the most frequent problems I've bumped
into are unconditional deference of the pointer even though
it's NULL, and hangs as a result of a lost event where memory
for the event couldn't be allocated.  Two sysctls are added:

debug.malloc.failure_rate

  How often to generate a failure: if set to 0 (default), this
  feature is disabled.  Otherwise, the frequency of failures --
  I've been using 10 (one in ten mallocs fails), but other
  popular settings might be much lower or much higher.

debug.malloc.failure_count

  Number of times a coerced malloc failure has occurred as a
  result of this feature.  Useful for tracking what might have
  happened and whether failures are being generated.

Useful possible additions: tying failure rate to malloc type,
printfs indicating the thread that experienced the coerced
failure.

Reviewed by:	jeffr, jhb
This commit is contained in:
Robert Watson 2003-03-26 20:18:40 +00:00
parent 90836fcf7d
commit eae870cdb4
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=112689
2 changed files with 27 additions and 0 deletions
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1
sys/conf/options
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@ -473,6 +473,7 @@ VM_KMEM_SIZE opt_vm.h
VM_KMEM_SIZE_SCALE opt_vm.h
VM_KMEM_SIZE_MAX opt_vm.h
NO_SWAPPING opt_vm.h
MALLOC_MAKE_FAILURES opt_vm.h
MALLOC_PROFILE opt_vm.h
PQ_NOOPT opt_vmpage.h
PQ_NORMALCACHE opt_vmpage.h

26
sys/kern/kern_malloc.c
View File

@ -138,6 +138,23 @@ static int sysctl_kern_malloc(SYSCTL_HANDLER_ARGS);
/* time_uptime of last malloc(9) failure */
static time_t t_malloc_fail;
#ifdef MALLOC_MAKE_FAILURES
/*
* Causes malloc failures every (n) mallocs with M_NOWAIT. If set to 0,
* doesn't cause failures.
*/
SYSCTL_NODE(_debug, OID_AUTO, malloc, CTLFLAG_RD, 0,
"Kernel malloc debugging options");
static int malloc_failure_rate;
static int malloc_nowait_count;
static int malloc_failure_count;
SYSCTL_INT(_debug_malloc, OID_AUTO, failure_rate, CTLFLAG_RW,
&malloc_failure_rate, 0, "Every (n) mallocs with M_NOWAIT will fail");
SYSCTL_INT(_debug_malloc, OID_AUTO, failure_count, CTLFLAG_RD,
&malloc_failure_count, 0, "Number of imposed M_NOWAIT malloc failures");
#endif
int
malloc_last_fail(void)
{
@ -187,6 +204,15 @@ malloc(size, type, flags)
#if 0
if (size == 0)
Debugger("zero size malloc");
#endif
#ifdef MALLOC_MAKE_FAILURES
if ((flags & M_NOWAIT) && (malloc_failure_rate != 0)) {
atomic_add_int(&malloc_nowait_count, 1);
if ((malloc_nowait_count % malloc_failure_rate) == 0) {
atomic_add_int(&malloc_failure_count, 1);
return (NULL);
}
}
#endif
if (flags & M_WAITOK)
KASSERT(curthread->td_intr_nesting_level == 0,