Dead lock contention for DAX-mmap page fault with snapshot taking

Open Andiry opened this issue 8 years ago • 1 comments

Reproduce steps:

Run whisper vacation workload, then take a snapshot.

Root cause:

We do not allow DAX-COW page fault during snapshot taking. It will wait for snapshot taking finished.

Process 1 Process 2

Snapshot taking start

                                                      Page fault
                                                      down_write(&mm->mmap_sem)
                                                      // nova_restore_page_write

                                                      // waiting for snapshot complete in nova_mmap_to_new_blocks()
                                                      // Stuck here

down_write(&mm->mmap_sem) // nova_set_vma_read // Stuck here

Sep 13 '17 19:09 Andiry

Am I mistaken, or is this still not resolved?

Jun 25 '21 05:06 derrickgreenspan