Commit 04a13c7c authored Sep 01, 2009 by Tejun Heo

percpu: don't assume existence of cpu0



percpu incorrectly assumed that cpu0 was always there which led to the
following warning and eventual oops on sparc machines w/o cpu0.

  WARNING: at mm/percpu.c:651 pcpu_map+0xdc/0x100()
  Modules linked in:
  Call Trace:
    [000000000045eb70] warn_slowpath_common+0x50/0xa0
    [000000000045ebdc] warn_slowpath_null+0x1c/0x40
    [00000000004d493c] pcpu_map+0xdc/0x100
    [00000000004d59a4] pcpu_alloc+0x3e4/0x4e0
    [00000000004d5af8] __alloc_percpu+0x18/0x40
    [00000000005b112c] __percpu_counter_init+0x4c/0xc0
  ...
  Unable to handle kernel NULL pointer dereference
  ...
   I7: <sysfs_new_dirent+0x30/0x120>
   Disabling lock debugging due to kernel taint
   Caller[000000000053c1b0]: sysfs_new_dirent+0x30/0x120
   Caller[000000000053c7a4]: create_dir+0x24/0xc0
   Caller[000000000053c870]: sysfs_create_dir+0x30/0x80
   Caller[00000000005990e8]: kobject_add_internal+0xc8/0x200
  ...
   Kernel panic - not syncing: Attempted to kill the idle task!

This patch fixes the problem by backporting parts from devel branch to
make percpu core not depend on the existence of cpu0.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Meelis Roos <mroos@linux.ee>
Cc: David Miller <davem@davemloft.net>

parent 142d44b0

mm/percpu.c

+14 −1

Original line number	Diff line number	Diff line
		@@ -197,7 +197,12 @@ static unsigned long pcpu_chunk_addr(struct pcpu_chunk *chunk,
		static bool pcpu_chunk_page_occupied(struct pcpu_chunk *chunk,
		int page_idx)
		{
		return *pcpu_chunk_pagep(chunk, 0, page_idx) != NULL;
		/*
		* Any possible cpu id can be used here, so there's no need to
		* worry about preemption or cpu hotplug.
		*/
		return *pcpu_chunk_pagep(chunk, raw_smp_processor_id(),
		page_idx) != NULL;
		}

		/* set the pointer to a chunk in a page struct */
		@@ -297,6 +302,14 @@ static struct pcpu_chunk pcpu_chunk_addr_search(void addr)
		return pcpu_first_chunk;
		}

		/*
		* The address is relative to unit0 which might be unused and
		* thus unmapped. Offset the address to the unit space of the
		* current processor before looking it up in the vmalloc
		* space. Note that any possible cpu id can be used here, so
		* there's no need to worry about preemption or cpu hotplug.
		*/
		addr += raw_smp_processor_id() * pcpu_unit_size;
		return pcpu_get_page_chunk(vmalloc_to_page(addr));
		}

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