mirror of https://gitee.com/openkylin/linux.git
87bf91d39b
hugetlbfs page faults can race with truncate and hole punch operations. Current code in the page fault path attempts to handle this by 'backing out' operations if we encounter the race. One obvious omission in the current code is removing a page newly added to the page cache. This is pretty straight forward to address, but there is a more subtle and difficult issue of backing out hugetlb reservations. To handle this correctly, the 'reservation state' before page allocation needs to be noted so that it can be properly backed out. There are four distinct possibilities for reservation state: shared/reserved, shared/no-resv, private/reserved and private/no-resv. Backing out a reservation may require memory allocation which could fail so that needs to be taken into account as well. Instead of writing the required complicated code for this rare occurrence, just eliminate the race. i_mmap_rwsem is now held in read mode for the duration of page fault processing. Hold i_mmap_rwsem in write mode when modifying i_size. In this way, truncation can not proceed when page faults are being processed. In addition, i_size will not change during fault processing so a single check can be made to ensure faults are not beyond (proposed) end of file. Faults can still race with hole punch, but that race is handled by existing code and the use of hugetlb_fault_mutex. With this modification, checks for races with truncation in the page fault path can be simplified and removed. remove_inode_hugepages no longer needs to take hugetlb_fault_mutex in the case of truncation. Comments are expanded to explain reasoning behind locking. Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Hugh Dickins <hughd@google.com> Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Prakash Sangappa <prakash.sangappa@oracle.com> Link: http://lkml.kernel.org/r/20200316205756.146666-3-mike.kravetz@oracle.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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