From: Pasha Tatashin <tatashin@xxxxxxxxxx> Changelog: - use the "fetch" variant instead of "return" of atomic instructions - allow negative values, as we are using all 32-bits of _refcount. It is hard to root cause _refcount problems, because they usually manifest after the damage has occurred. Yet, they can lead to catastrophic failures such memory corruptions. There were a number of refcount related issues discovered recently [1], [2], [3]. Improve debugability by adding more checks that ensure that page->_refcount never turns negative (i.e. double free does not happen, or free after freeze etc). - Check for overflow and underflow right from the functions that modify _refcount - Remove set_page_count(), so we do not unconditionally overwrite _refcount with an unrestrained value - Trace return values in all functions that modify _refcount Applies against next-20211116. Previous verions: RFCv1: https://lore.kernel.org/all/20211026173822.502506-1-pasha.tatashin@xxxxxxxxxx [1] https://lore.kernel.org/all/xr9335nxwc5y.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxx [2] https://lore.kernel.org/all/1582661774-30925-2-git-send-email-akaher@xxxxxxxxxx [3] https://lore.kernel.org/all/20210622021423.154662-3-mike.kravetz@xxxxxxxxxx Pasha Tatashin (10): mm: page_ref_add_unless() does not trace 'u' argument mm: add overflow and underflow checks for page->_refcount mm: Avoid using set_page_count() in set_page_recounted() mm: remove set_page_count() from page_frag_alloc_align mm: avoid using set_page_count() when pages are freed into allocator mm: rename init_page_count() -> page_ref_init() mm: remove set_page_count() mm: simplify page_ref_* functions mm: do not use atomic_set_release in page_ref_unfreeze() mm: use atomic_cmpxchg_acquire in page_ref_freeze(). arch/m68k/mm/motorola.c | 2 +- include/linux/mm.h | 2 +- include/linux/page_ref.h | 159 +++++++++++++++----------------- include/trace/events/page_ref.h | 99 +++++++++++++++----- mm/debug_page_ref.c | 30 ++---- mm/internal.h | 6 +- mm/page_alloc.c | 19 ++-- 7 files changed, 180 insertions(+), 137 deletions(-) -- 2.34.0.rc1.387.gb447b232ab-goog
