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Re: [lvm-devel] clvmd coredump issue



Dne 24.4.2014 08:58, Liuhua Wang napsal(a):
Hi, list

I have encountered a coredump when start clvmd on ppc64 as followed:

#p $pc
$1 = (void (*)()) 0x10070c18
#bt
#0  0x0000000010070c18 in _allocate_memory () at mm/memlock.c:130
#1  0x0000000010070d38 in _lock_mem (cmd=<optimized out>) at mm/memlock.c:310
#2  _lock_mem_if_needed (cmd=0x10104f40) at mm/memlock.c:387
#3  0x0000000010011358 in init_clvm (excl_uuid=<optimized out>) at
lvm-functions.c:919
#4  0x000000001000f47c in lvm_thread_fn (arg=0xfffcaf4e530) at clvmd.c:2020
#5  0x00000fff9df6c67c in .start_thread () from /lib64/power6/libpthread.so.0
#6  0x00000fff9de7643c in .__clone () from /lib64/power6/libc.so.6


When the followed four lines are commented then the problem is ok.
I suppose the problem is probably because of alloca.

static void _allocate_memory(void)
{
	void *stack_mem, *temp_malloc_mem;
	struct rlimit limit;

	/* Check if we could preallocate requested stack */
-	if ((getrlimit (RLIMIT_STACK, &limit) == 0) &&
-	    ((_size_stack * 2) < limit.rlim_cur) &&
-         ((stack_mem = alloca(_size_stack))))
-	   _touch_memory(stack_mem, _size_stack);
	/* FIXME else warn user setting got ignored */

	if ((temp_malloc_mem = malloc(_size_malloc_tmp)))
		_touch_memory(temp_malloc_mem, _size_malloc_tmp);

	if ((_malloc_mem = malloc(_size_malloc)))
		_touch_memory(_malloc_mem, _size_malloc);

	free(temp_malloc_mem);
}

My questions are:
1. Can we delete the four lines, since it is just PREallocate?
2. What is the purpose of _touch_memory()
3. why do first malloc temp_malloc_mem but then free it?

Any information is very appreciated.

The memory use in lvm2 has deeper logic.

The idea behind preallocation and touching memory is - to preallocate memory pages and enforce their physical allocation for stack & heap - before the memory is mlock()-ed into RAM.

Since the suspend may free i.e. swap device - all the code parts which run in suspend needs to be locked in RAM.

Now back to powerpc issue - check why it's crashing -  is the rlim_cur  wrong?
Stack size is too big ?

Code will not be removed it needs to be fixed for powerpc.

Zdenek



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