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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 7665A40012 X-Stat-Signature: xj6qeg4jitue55167uiwykwezgej5fmr X-HE-Tag: 1770115559-198255 X-HE-Meta: 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 Vz+TMlKR 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 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: List-Subscribe: List-Unsubscribe: If hmm_range_fault() fails a folio_trylock() in do_swap_page, trying to acquire the lock of a device-private folio for migration, to ram, the function will spin until it succeeds grabbing the lock. However, if the process holding the lock is depending on a work item to be completed, which is scheduled on the same CPU as the spinning hmm_range_fault(), that work item might be starved and we end up in a livelock / starvation situation which is never resolved. This can happen, for example if the process holding the device-private folio lock is stuck in migrate_device_unmap()->lru_add_drain_all() The lru_add_drain_all() function requires a short work-item to be run on all online cpus to complete. A prerequisite for this to happen is: a) Both zone device and system memory folios are considered in migrate_device_unmap(), so that there is a reason to call lru_add_drain_all() for a system memory folio while a folio lock is held on a zone device folio. b) The zone device folio has an initial mapcount > 1 which causes at least one migration PTE entry insertion to be deferred to try_to_migrate(), which can happen after the call to lru_add_drain_all(). c) No or voluntary only preemption. This all seems pretty unlikely to happen, but indeed is hit by the "xe_exec_system_allocator" igt test. Resolve this by waiting for the folio to be unlocked if the folio_trylock() fails in the do_swap_page() function. Future code improvements might consider moving the lru_add_drain_all() call in migrate_device_unmap() to be called *after* all pages have migration entries inserted. That would eliminate also b) above. v2: - Instead of a cond_resched() in the hmm_range_fault() function, eliminate the problem by waiting for the folio to be unlocked in do_swap_page() (Alistair Popple, Andrew Morton) Suggested-by: Alistair Popple Fixes: 1afaeb8293c9 ("mm/migrate: Trylock device page in do_swap_page") Cc: Ralph Campbell Cc: Christoph Hellwig Cc: Jason Gunthorpe Cc: Jason Gunthorpe Cc: Leon Romanovsky Cc: Andrew Morton Cc: Matthew Brost Cc: John Hubbard Cc: Alistair Popple Cc: linux-mm@kvack.org Cc: Signed-off-by: Thomas Hellström Cc: # v6.15+ --- mm/memory.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/memory.c b/mm/memory.c index da360a6eb8a4..ed20da5570d5 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4684,7 +4684,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) unlock_page(vmf->page); put_page(vmf->page); } else { - pte_unmap_unlock(vmf->pte, vmf->ptl); + pte_unmap(vmf->pte); + migration_entry_wait_on_locked(entry, vmf->ptl); } } else if (softleaf_is_hwpoison(entry)) { ret = VM_FAULT_HWPOISON; -- 2.52.0