Searched hist:"3 a47c54f" (Results 1 – 4 of 4) sorted by relevance
| /openbmc/linux/fs/hugetlbfs/ |
| H A D | inode.c | 3a47c54f Wed Sep 14 17:18:03 CDT 2022 Mike Kravetz <mike.kravetz@oracle.com> hugetlbfs: revert use i_mmap_rwsem for more pmd sharing synchronization
Commit c0d0381ade79 ("hugetlbfs: use i_mmap_rwsem for more pmd sharing
synchronization") added code to take i_mmap_rwsem in read mode for the
duration of fault processing. However, this has been shown to cause
performance/scaling issues. Revert the code and go back to only taking
the semaphore in huge_pmd_share during the fault path.
Keep the code that takes i_mmap_rwsem in write mode before calling
try_to_unmap as this is required if huge_pmd_unshare is called.
NOTE: Reverting this code does expose the following race condition.
Faulting thread Unsharing thread
... ...
ptep = huge_pte_offset()
or
ptep = huge_pte_alloc()
...
i_mmap_lock_write
lock page table
ptep invalid <------------------------ huge_pmd_unshare()
Could be in a previously unlock_page_table
sharing process or worse i_mmap_unlock_write
...
ptl = huge_pte_lock(ptep)
get/update pte
set_pte_at(pte, ptep)
It is unknown if the above race was ever experienced by a user. It was
discovered via code inspection when initially addressed.
In subsequent patches, a new synchronization mechanism will be added to
coordinate pmd sharing and eliminate this race.
Link: https://lkml.kernel.org/r/20220914221810.95771-3-mike.kravetz@oracle.com
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: James Houghton <jthoughton@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Prakash Sangappa <prakash.sangappa@oracle.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
|
| /openbmc/linux/mm/ |
| H A D | userfaultfd.c | 3a47c54f Wed Sep 14 17:18:03 CDT 2022 Mike Kravetz <mike.kravetz@oracle.com> hugetlbfs: revert use i_mmap_rwsem for more pmd sharing synchronization
Commit c0d0381ade79 ("hugetlbfs: use i_mmap_rwsem for more pmd sharing
synchronization") added code to take i_mmap_rwsem in read mode for the
duration of fault processing. However, this has been shown to cause
performance/scaling issues. Revert the code and go back to only taking
the semaphore in huge_pmd_share during the fault path.
Keep the code that takes i_mmap_rwsem in write mode before calling
try_to_unmap as this is required if huge_pmd_unshare is called.
NOTE: Reverting this code does expose the following race condition.
Faulting thread Unsharing thread
... ...
ptep = huge_pte_offset()
or
ptep = huge_pte_alloc()
...
i_mmap_lock_write
lock page table
ptep invalid <------------------------ huge_pmd_unshare()
Could be in a previously unlock_page_table
sharing process or worse i_mmap_unlock_write
...
ptl = huge_pte_lock(ptep)
get/update pte
set_pte_at(pte, ptep)
It is unknown if the above race was ever experienced by a user. It was
discovered via code inspection when initially addressed.
In subsequent patches, a new synchronization mechanism will be added to
coordinate pmd sharing and eliminate this race.
Link: https://lkml.kernel.org/r/20220914221810.95771-3-mike.kravetz@oracle.com
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: James Houghton <jthoughton@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Prakash Sangappa <prakash.sangappa@oracle.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
|
| H A D | rmap.c | 3a47c54f Wed Sep 14 17:18:03 CDT 2022 Mike Kravetz <mike.kravetz@oracle.com> hugetlbfs: revert use i_mmap_rwsem for more pmd sharing synchronization
Commit c0d0381ade79 ("hugetlbfs: use i_mmap_rwsem for more pmd sharing
synchronization") added code to take i_mmap_rwsem in read mode for the
duration of fault processing. However, this has been shown to cause
performance/scaling issues. Revert the code and go back to only taking
the semaphore in huge_pmd_share during the fault path.
Keep the code that takes i_mmap_rwsem in write mode before calling
try_to_unmap as this is required if huge_pmd_unshare is called.
NOTE: Reverting this code does expose the following race condition.
Faulting thread Unsharing thread
... ...
ptep = huge_pte_offset()
or
ptep = huge_pte_alloc()
...
i_mmap_lock_write
lock page table
ptep invalid <------------------------ huge_pmd_unshare()
Could be in a previously unlock_page_table
sharing process or worse i_mmap_unlock_write
...
ptl = huge_pte_lock(ptep)
get/update pte
set_pte_at(pte, ptep)
It is unknown if the above race was ever experienced by a user. It was
discovered via code inspection when initially addressed.
In subsequent patches, a new synchronization mechanism will be added to
coordinate pmd sharing and eliminate this race.
Link: https://lkml.kernel.org/r/20220914221810.95771-3-mike.kravetz@oracle.com
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: James Houghton <jthoughton@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Prakash Sangappa <prakash.sangappa@oracle.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
|
| H A D | hugetlb.c | 3a47c54f Wed Sep 14 17:18:03 CDT 2022 Mike Kravetz <mike.kravetz@oracle.com> hugetlbfs: revert use i_mmap_rwsem for more pmd sharing synchronization
Commit c0d0381ade79 ("hugetlbfs: use i_mmap_rwsem for more pmd sharing
synchronization") added code to take i_mmap_rwsem in read mode for the
duration of fault processing. However, this has been shown to cause
performance/scaling issues. Revert the code and go back to only taking
the semaphore in huge_pmd_share during the fault path.
Keep the code that takes i_mmap_rwsem in write mode before calling
try_to_unmap as this is required if huge_pmd_unshare is called.
NOTE: Reverting this code does expose the following race condition.
Faulting thread Unsharing thread
... ...
ptep = huge_pte_offset()
or
ptep = huge_pte_alloc()
...
i_mmap_lock_write
lock page table
ptep invalid <------------------------ huge_pmd_unshare()
Could be in a previously unlock_page_table
sharing process or worse i_mmap_unlock_write
...
ptl = huge_pte_lock(ptep)
get/update pte
set_pte_at(pte, ptep)
It is unknown if the above race was ever experienced by a user. It was
discovered via code inspection when initially addressed.
In subsequent patches, a new synchronization mechanism will be added to
coordinate pmd sharing and eliminate this race.
Link: https://lkml.kernel.org/r/20220914221810.95771-3-mike.kravetz@oracle.com
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: James Houghton <jthoughton@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Prakash Sangappa <prakash.sangappa@oracle.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
|