mm/damon/vaddr: do not repeat pte_offset_map_lock() until success

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commit b93af2cc8e upstream.

DAMON's virtual address space operation set implementation (vaddr) calls
pte_offset_map_lock() inside the page table walk callback function.  This
is for reading and writing page table accessed bits.  If
pte_offset_map_lock() fails, it retries by returning the page table walk
callback function with ACTION_AGAIN.

pte_offset_map_lock() can continuously fail if the target is a pmd
migration entry, though.  Hence it could cause an infinite page table walk
if the migration cannot be done until the page table walk is finished.
This indeed caused a soft lockup when CPU hotplugging and DAMON were
running in parallel.

Avoid the infinite loop by simply not retrying the page table walk.  DAMON
is promising only a best-effort accuracy, so missing access to such pages
is no problem.

Link: https://lkml.kernel.org/r/20250930004410.55228-1-sj@kernel.org
Fixes: 7780d04046 ("mm/pagewalkers: ACTION_AGAIN if pte_offset_map_lock() fails")
Signed-off-by: SeongJae Park <sj@kernel.org>
Reported-by: Xinyu Zheng <zhengxinyu6@huawei.com>
Closes: https://lore.kernel.org/20250918030029.2652607-1-zhengxinyu6@huawei.com
Acked-by: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>	[6.5+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

...

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SeongJae Park 2025-09-29 17:44:09 -07:00 • committed by Greg Kroah-Hartman

parent b9737c2063

commit ac42320ec8

1 changed files with 2 additions and 6 deletions

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mm/damon/vaddr.c

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