Commit e709accc authored Jul 24, 2019 by Jason Gunthorpe

mm/hmm: comment on VM_FAULT_RETRY semantics in handle_mm_fault

The magic dropping of mmap_sem when handle_mm_fault returns VM_FAULT_RETRY
is rather subtile.  Add a comment explaining it.

Link: https://lore.kernel.org/r/20190724065258.16603-8-hch@lst.de


Tested-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
[hch: wrote a changelog]
Signed-off-by: Christoph Hellwig <hch@lst.de>

parent f32471e2

mm/hmm.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -301,8 +301,10 @@ static int hmm_vma_do_fault(struct mm_walk *walk, unsigned long addr,
		flags \|= hmm_vma_walk->block ? 0 : FAULT_FLAG_ALLOW_RETRY;
		flags \|= write_fault ? FAULT_FLAG_WRITE : 0;
		ret = handle_mm_fault(vma, addr, flags);
		if (ret & VM_FAULT_RETRY)
		if (ret & VM_FAULT_RETRY) {
		/* Note, handle_mm_fault did up_read(&mm->mmap_sem)) */
		return -EAGAIN;
		}
		if (ret & VM_FAULT_ERROR) {
		*pfn = range->values[HMM_PFN_ERROR];
		return -EFAULT;

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