From: Wei Yang During stress testing with stress-ng on a 256-CPU system, a softlockup was observed when madvise(MADV_COLD) was called on a 31GB memory region backed by transparent hugepages. The region contains 15935 THP PMD entries, and the softlockup was triggered after 14485 of them had been processed. The THP branch of madvise_cold_or_pageout_pte_range() has no scheduling point. walk_pmd_range() invokes it once per 2MB PMD entry with no cond_resched() anywhere in the loop. Each iteration calls pmdp_invalidate() which issues a synchronous TLB shootdown (dsb ish) waiting for all CPUs to acknowledge. This operation can be time-consuming under heavy system load, causing the accumulated time across all PMD entries to exceed the softlockup threshold (20s) and panic when softlockup_panic=1. On a CONFIG_PREEMPT_NONE=y kernel, there is no other opportunity to reschedule during this entire traversal. The regular PTE path already has an unconditional cond_resched() at the function tail (introduced by commit 9c276cc65a58 ("mm: introduce MADV_COLD") and commit 1a4e58cce84e ("mm: introduce MADV_PAGEOUT") when MADV_COLD and MADV_PAGEOUT were first introduced) and a conditional one inside the loop (commit b2f557a21bc8 ("mm/madvise: add cond_resched() in madvise_cold_or_pageout_pte_range()")). The THP branch never received equivalent treatment. Fix by adding cond_resched() at the huge_unlock exit path after spin_unlock(ptl) and reclaim_pages(), which is the single exit point for all goto paths in the THP branch. Crash log: watchdog: BUG: soft lockup - CPU#63 stuck for 23s! [stress-ng-vm:1665914] ... Call trace: pmdp_invalidate+0x48/0x68 madvise_cold_or_pageout_pte_range+0x84c/0xb00 walk_pmd_range.isra.0+0x1ac/0x3b0 walk_pud_range+0x120/0x190 walk_pgd_range+0x170/0x1b8 __walk_page_range+0x184/0x198 walk_page_range_vma+0x94/0x128 madvise_cold+0xd8/0x198 madvise_vma_behavior+0x234/0x638 madvise_walk_vmas.constprop.0+0xdc/0x210 madvise_do_behavior+0xa8/0x328 do_madvise+0xd8/0x140 __arm64_sys_madvise+0x2c/0xe0 Signed-off-by: Wei Yang --- mm/madvise.c | 1 + 1 file changed, 1 insertion(+) diff --git a/mm/madvise.c b/mm/madvise.c index eeee82cf2b3f..0755e6d99757 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -450,6 +450,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd, spin_unlock(ptl); if (pageout) reclaim_pages(&folio_list); + cond_resched(); return 0; } -- 2.43.5