2009-03-10 10:27:54 Heap memory alloc failure crash

Hari Prasad (INDIA)

Message: 70701

Hi,

In uClinux, suppose a malloc call fails for the requested memory size, kernel crashes instead of returning a NULL pointer. Because of this, we are not able to ensure the stability of our application. Could you please let us know if there is anything to be changed in the kernel config by which kernel doesn't crash but just returns NULL if the malloc fails. If there is no kernel config, is there any other way to handle this problem.

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2009-03-10 12:53:44 Re: Heap memory alloc failure crash

Robin Getz (UNITED STATES)

Message: 70710

Hari:

This is not uClinux specific - this is the same way that it works on your desktop. It is just your desktop has lots more memory before it becomes "full".

The kernel memory allocator doesn't know if the request is coming from the kernel, or from userspace - so it kills something.

-Robin

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2009-03-11 09:17:08 Re: Heap memory alloc failure crash

Hari Prasad (INDIA)

Message: 70773

Hi Robin,

Thanks for the reply. I would like to know if there is any way that we can program the kernel to gracefully exit rather than to crash as it brings in a lot of indeterminism in our application if the kernel can crash anytime.

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2009-03-11 09:37:48 Re: Heap memory alloc failure crash

Mike Frysinger (UNITED STATES)

Message: 70775

the kernel isnt crashing, nor does the kernel "exit". your application ran out of memory and so it was killed.

there is discussion on lkml about adding a "low memory" notification system, but that isnt implemented yet

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2009-03-11 12:50:04 Re: Heap memory alloc failure crash

Marco Rohleder (GERMANY)

Message: 70786

What he just wanted to ask is:

if malloc() fails, because of not enough memory left, you see a stack trace instead of malloc() just returning NULL

Why ?

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2009-03-11 12:59:36 Re: Heap memory alloc failure crash

Mike Frysinger (UNITED STATES)

Message: 70787

Robin already explained why

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2009-03-12 02:05:50 Re: Heap memory alloc failure crash

Hari Prasad (INDIA)

Message: 70813

Robin and Mike,

If our application asks for memory and is not available, we have routines to safely exit the app incase malloc fails. Isnt it dangerous from the app perspective when you say "so it kills something"?

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2009-03-12 02:29:43 Re: Heap memory alloc failure crash

Mike Frysinger (UNITED STATES)

Message: 70820

that is how it works

you can wait for the aforementioned "low mem" system to be developed, or you can try to write your own in the meantime