sched/isolation: Defer freeing of cpumask memblock memory to initcall

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When testing a linux-next kernel with commit 59bd1d914b ("memblock:
warn when freeing reserved memory before memory map is initialized"),
the following warning was hit when there was a "nohz_full" kernel boot
parameter.

  Cannot free reserved memory because of deferred initialization of the memory map
  WARNING: mm/memblock.c:904 at __free_reserved_area+0xde/0xf0, CPU#0: swapper/0/0
    :
  Call Trace:
   <TASK>
   memblock_phys_free+0xcb/0x100
   housekeeping_init+0x14c/0x170
   start_kernel+0x207/0x450
   x86_64_start_reservations+0x24/0x30
   x86_64_start_kernel+0xda/0xe0
   common_startup_64+0x13e/0x141
   </TASK>

IOW, we shouldn't free memblock allocated memory so early
in the boot process when memory map isn't fully initialized in
deferred_init_memmap().

Fix it by saving the housekeeping cpumask memblock memory to be
freed into a llist free list in housekeeping_init() and add a new
housekeeping_late_init() helper to defer the actual freeing of memblock
memory to when initcall's are being processed. The cpumask memblock
memory is treated as a llist_node with the size of a "long" type which
is also smallest cpumask size that can be allocated.

The non-atomic version of the llist APIs are used as there is no
contention.

This commit depends on the presence of commit 7c2eee9c13 ("memblock:
don't touch memblock arrays when memblock_free() is called late")
to prevent a KASAN UAF bug report [1].

 [1] https://lore.kernel.org/lkml/20260505051821.1107133-1-longman@redhat.com/

Fixes: 27c3a5967f ("sched/isolation: Convert housekeeping cpumasks to rcu pointers")
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Phil Auld <pauld@redhat.com>
Link: https://patch.msgid.link/20260701195810.477326-1-longman@redhat.com

...

This commit is contained in:

Waiman Long 2026-07-01 15:58:10 -04:00 • committed by Peter Zijlstra

parent f2c2ba7219

commit 2b58c749b8

1 changed files with 15 additions and 1 deletions

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kernel/sched/isolation.c

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