On 8/3/20 3:52 PM, Matthew Wilcox wrote:
On Mon, Aug 03, 2020 at 03:43:35PM -0700, Mike Kravetz wrote:
Commit c0d0381ade79 ("hugetlbfs: use i_mmap_rwsem for more pmd sharing synchronization") requires callers of huge_pte_alloc to hold i_mmap_rwsem in at least read mode. This is because the explicit locking in huge_pmd_share (called by huge_pte_alloc) was removed. When restructuring the code, the call to huge_pte_alloc in the else block at the beginning of hugetlb_fault was missed.
Should we have a call to mmap_assert_locked() in huge_pte_alloc(), at least the generic one?
That is the wrong semaphore.
However, I was not aware of the checks for a semaphore being held as is done in rwsem_is_locked(). That would have caught this when the original code was changed. Thanks for pointing this out.
Let me update the patch and add checks to huge_pmd_share().