Re: How to analyze kmemleak message?

Hello.

Thank you for explanation.

Catalin Marinas wrote:
As Pekka said, they refer to the place where the object was allocated.
OK. The trace shows where that memory was allocated.

This object can no longer be found to be referred by other objects or
from the data section, hence it is assumed to be a leak (it could, as
well, be a false positive, transient or not).
Kmemleak scans all data section for addresses returned by kmalloc() etc.

void *p1;

void foo(void)
{
void *p2 = kmalloc(1, GFP_KERNEL);
p1 = kmalloc(1, GFP_KERNEL);
}

"p1" will be reported by default.
To report "p2", we need to write "stack=on" to /sys/kernel/debug/kmemleak .
Is this correct?

Basically, you need check
where the pointer returned by kmalloc/kmem_cache_alloc etc. should be
stored and whether it can still be referred from that place (or a
different one) later.

Kmemleak tries to avoid the reporting of transient leaks by only
reporting objects with a life time of more than 5 seconds.
kjournald's commit interval (default to 5 sec?) + a few seconds
might be better. (No reason. Just my feeling.)

To make sure
the reports you got aren't transient leaks, you can read
the /sys/kernel/debug/kmemleak file a few times to see whether they
disappear.
Well, I couldn't check /sys/kernel/debug/kmemleak etc. because
I couldn't reach login prompt.

There is a Documentation/kmemleak.txt file where you may find some
useful information.
I see.

I have a question. My module uses kmalloc(PATH_MAX, GFP_KERNEL) which
won't be released by kfree(). I count up how many bytes are allocated but
I don't want kmemleak to report such memory as memory leaks.
Can I do so by

void bar(void)
{
static void *p;
if (!p) {
p = kmalloc(PATH_MAX, GFP_KERNEL);
kmemleak_not_leak(p);
}
...
}

(or kmemleak_ignore() (which one to use and how to use))?

Regards.
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