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secretmem: Prevent secretmem_users from wrapping to zero
Commit 1108605 ("mm/secretmem: use refcount_t instead of atomic_t") attempted to fix the problem of secretmem_users wrapping to zero and allowing suspend once again. But it was reverted in commit 87066fd ("Revert 'mm/secretmem: use refcount_t instead of atomic_t'") because of the problems it caused - a refcount_t was not semantically the right type to use. Instead prevent secretmem_users from wrapping to zero by forbidding new users if the number of users has wrapped from positive to negative. This stops a long way short of reaching the necessary 4 billion users where it wraps to zero again, so there's no need to be clever with special anti-wrap types or checking the return value from atomic_inc(). Signed-off-by: Matthew Wilcox (Oracle) <[email protected]> Cc: Jordy Zomer <[email protected]> Cc: Kees Cook <[email protected]>, Cc: James Bottomley <[email protected]> Cc: Mike Rapoport <[email protected]> Cc: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
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