coredump: fix race condition between collapse_huge_page() and core dumping
When fixing the race conditions between the coredump and the mmap_sem holders outside the context of the process, we focused on mmget_not_zero()/get_task_mm() callers in04f5866e41
("coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping"), but those aren't the only cases where the mmap_sem can be taken outside of the context of the process as Michal Hocko noticed while backporting that commit to older -stable kernels. If mmgrab() is called in the context of the process, but then the mm_count reference is transferred outside the context of the process, that can also be a problem if the mmap_sem has to be taken for writing through that mm_count reference. khugepaged registration calls mmgrab() in the context of the process, but the mmap_sem for writing is taken later in the context of the khugepaged kernel thread. collapse_huge_page() after taking the mmap_sem for writing doesn't modify any vma, so it's not obvious that it could cause a problem to the coredump, but it happens to modify the pmd in a way that breaks an invariant that pmd_trans_huge_lock() relies upon. collapse_huge_page() needs the mmap_sem for writing just to block concurrent page faults that call pmd_trans_huge_lock(). Specifically the invariant that "!pmd_trans_huge()" cannot become a "pmd_trans_huge()" doesn't hold while collapse_huge_page() runs. The coredump will call __get_user_pages() without mmap_sem for reading, which eventually can invoke a lockless page fault which will need a functional pmd_trans_huge_lock(). So collapse_huge_page() needs to use mmget_still_valid() to check it's not running concurrently with the coredump... as long as the coredump can invoke page faults without holding the mmap_sem for reading. This has "Fixes: khugepaged" to facilitate backporting, but in my view it's more a bug in the coredump code that will eventually have to be rewritten to stop invoking page faults without the mmap_sem for reading. So the long term plan is still to drop all mmget_still_valid(). Link: http://lkml.kernel.org/r/20190607161558.32104-1-aarcange@redhat.com Fixes:ba76149f47
("thp: khugepaged") Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reported-by: Michal Hocko <mhocko@suse.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Jann Horn <jannh@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Mike Rapoport <rppt@linux.vnet.ibm.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Peter Xu <peterx@redhat.com> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
parent
0874bb49bb
commit
59ea6d06cf
|
@ -54,6 +54,10 @@ static inline void mmdrop(struct mm_struct *mm)
|
||||||
* followed by taking the mmap_sem for writing before modifying the
|
* followed by taking the mmap_sem for writing before modifying the
|
||||||
* vmas or anything the coredump pretends not to change from under it.
|
* vmas or anything the coredump pretends not to change from under it.
|
||||||
*
|
*
|
||||||
|
* It also has to be called when mmgrab() is used in the context of
|
||||||
|
* the process, but then the mm_count refcount is transferred outside
|
||||||
|
* the context of the process to run down_write() on that pinned mm.
|
||||||
|
*
|
||||||
* NOTE: find_extend_vma() called from GUP context is the only place
|
* NOTE: find_extend_vma() called from GUP context is the only place
|
||||||
* that can modify the "mm" (notably the vm_start/end) under mmap_sem
|
* that can modify the "mm" (notably the vm_start/end) under mmap_sem
|
||||||
* for reading and outside the context of the process, so it is also
|
* for reading and outside the context of the process, so it is also
|
||||||
|
|
|
@ -1004,6 +1004,9 @@ static void collapse_huge_page(struct mm_struct *mm,
|
||||||
* handled by the anon_vma lock + PG_lock.
|
* handled by the anon_vma lock + PG_lock.
|
||||||
*/
|
*/
|
||||||
down_write(&mm->mmap_sem);
|
down_write(&mm->mmap_sem);
|
||||||
|
result = SCAN_ANY_PROCESS;
|
||||||
|
if (!mmget_still_valid(mm))
|
||||||
|
goto out;
|
||||||
result = hugepage_vma_revalidate(mm, address, &vma);
|
result = hugepage_vma_revalidate(mm, address, &vma);
|
||||||
if (result)
|
if (result)
|
||||||
goto out;
|
goto out;
|
||||||
|
|
Loading…
Reference in a new issue