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s=arc-20220608; d=hostedemail.com; t=1661811869; a=rsa-sha256; cv=pass; b=twEk4I36rTGt1sBKVPTpZ3JjPG74EB7gGQdgiG7qO3PU8JSvLnbNywNADouDMqylPbDcPN YWO2wHfaunEosGSVfu+XQFEiPeV/AUkVpCpeoFO7I/kcOUytW0r6rFcLWHlejyPL/XhW+1 JR0flLjQmFuBe27h4kYZYCxAYLgqQO0= X-Stat-Signature: t7h8c9n3tcdsoaix4zzbh3kpasxfbfyt X-Rspamd-Queue-Id: 41BEF8005A Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=oracle.com header.s=corp-2022-7-12 header.b=QDTRnJq9; dkim=pass header.d=oracle.onmicrosoft.com header.s=selector2-oracle-onmicrosoft-com header.b=GC3g3zH+; arc=pass ("microsoft.com:s=arcselector9901:i=1"); spf=pass (imf30.hostedemail.com: domain of mike.kravetz@oracle.com designates 205.220.177.32 as permitted sender) smtp.mailfrom=mike.kravetz@oracle.com; dmarc=pass (policy=none) header.from=oracle.com X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1661811869-589769 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 08/27/22 17:30, Miaohe Lin wrote: > On 2022/8/25 1:57, Mike Kravetz wrote: > > Allocate a rw semaphore and hang off vm_private_data for > > synchronization use by vmas that could be involved in pmd sharing. Only > > add infrastructure for the new lock here. Actual use will be added in > > subsequent patch. > > > > Signed-off-by: Mike Kravetz > > > > > +static void hugetlb_vma_lock_free(struct vm_area_struct *vma) > > +{ > > + /* > > + * Only present in sharable vmas. See comment in > > + * __unmap_hugepage_range_final about the neeed to check both > > s/neeed/need/ > > > + * VM_SHARED and VM_MAYSHARE in free path > > I think there might be some wrong checks around this patch. As above comment said, we > need to check both flags, so we should do something like below instead? > > if (!(vma->vm_flags & (VM_MAYSHARE | VM_SHARED) == (VM_MAYSHARE | VM_SHARED))) > > > + */ Thanks. I will update. > > + if (!vma || !(vma->vm_flags & (VM_MAYSHARE | VM_SHARED))) > > + return; > > + > > + if (vma->vm_private_data) { > > + kfree(vma->vm_private_data); > > + vma->vm_private_data = NULL; > > + } > > +} > > + > > +static void hugetlb_vma_lock_alloc(struct vm_area_struct *vma) > > +{ > > + struct rw_semaphore *vma_sema; > > + > > + /* Only establish in (flags) sharable vmas */ > > + if (!vma || !(vma->vm_flags & VM_MAYSHARE)) > > + return; > > + > > + /* Should never get here with non-NULL vm_private_data */ > > We can get here with non-NULL vm_private_data when called from hugetlb_vm_op_open during fork? Right! In fork, We allocate a new semaphore in hugetlb_dup_vma_private, and then shortly after call hugetlb_vm_op_open. It works as is, and I can update the comment. However, I wonder if we should just clear vm_private_data in hugetlb_dup_vma_private and let hugetlb_vm_op_open do the allocation. > > Also there's one missing change on comment: > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index d0617d64d718..4bc844a1d312 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -863,7 +863,7 @@ __weak unsigned long vma_mmu_pagesize(struct vm_area_struct *vma) > * faults in a MAP_PRIVATE mapping. Only the process that called mmap() > * is guaranteed to have their future faults succeed. > * > - * With the exception of reset_vma_resv_huge_pages() which is called at fork(), > + * With the exception of hugetlb_dup_vma_private() which is called at fork(), > * the reserve counters are updated with the hugetlb_lock held. It is safe > * to reset the VMA at fork() time as it is not in use yet and there is no > * chance of the global counters getting corrupted as a result of the values. > > > Otherwise this patch looks good to me. Thanks. Will update, Thank you! -- Mike Kravetz