Make sure uvm_swap_get() always sleep and do not return and error.

If no memory was immediately available to decrypt (bounce) a page from swap
an error was returned to the fault handler which would result in processes
dying when a lot of memory pressure was applied to a system.

Note that reading from swap is always done synchronously.

ok beck@, kettenis@

diff --git a/sys/uvm/uvm_swap.c b/sys/uvm/uvm_swap.c
index 4915010..609c54c 100644 (file)
--- a/sys/uvm/uvm_swap.c
+++ b/sys/uvm/uvm_swap.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: uvm_swap.c,v 1.157 2022/06/28 19:19:34 mpi Exp $      */
+/*     $OpenBSD: uvm_swap.c,v 1.158 2022/06/28 19:39:54 mpi Exp $      */
 /*     $NetBSD: uvm_swap.c,v 1.40 2000/11/17 11:39:39 mrg Exp $        */
 
 /*
@@ -239,7 +239,7 @@ void sw_reg_start(struct swapdev *);
 int uvm_swap_io(struct vm_page **, int, int, int);
 
 void swapmount(void);
-int uvm_swap_allocpages(struct vm_page **, int);
+int uvm_swap_allocpages(struct vm_page **, int, int);
 
 #ifdef UVM_SWAP_ENCRYPT
 /* for swap encrypt */
@@ -288,7 +288,7 @@ uvm_swap_init(void)
            "swp vnd", NULL);
 
        /* allocate pages for OOM situations. */
-       error = uvm_swap_allocpages(oompps, SWCLUSTPAGES);
+       error = uvm_swap_allocpages(oompps, SWCLUSTPAGES, UVM_PLA_NOWAIT);
        KASSERT(error == 0);
 
        /* Setup the initial swap partition */
@@ -334,7 +334,7 @@ uvm_swap_initcrypt(struct swapdev *sdp, int npages)
 #endif /* UVM_SWAP_ENCRYPT */
 
 int
-uvm_swap_allocpages(struct vm_page **pps, int npages)
+uvm_swap_allocpages(struct vm_page **pps, int npages, int flags)
 {
        struct pglist   pgl;
        int error, i;
@@ -344,7 +344,7 @@ uvm_swap_allocpages(struct vm_page **pps, int npages)
        TAILQ_INIT(&pgl);
 again:
        error = uvm_pglistalloc(npages * PAGE_SIZE, dma_constraint.ucr_low,
-           dma_constraint.ucr_high, 0, 0, &pgl, npages, UVM_PLA_NOWAIT);
+           dma_constraint.ucr_high, 0, 0, &pgl, npages, flags);
        if (error && (curproc == uvm.pagedaemon_proc)) {
                mtx_enter(&oommtx);
                if (oom) {
@@ -394,6 +394,7 @@ uvm_swap_freepages(struct vm_page **pps, int npages)
        for (i = 0; i < npages; i++)
                uvm_pagefree(pps[i]);
        uvm_unlock_pageq();
+
 }
 
 #ifdef UVM_SWAP_ENCRYPT
@@ -1707,13 +1708,16 @@ uvm_swap_io(struct vm_page **pps, int startslot, int npages, int flags)
        }
 
        if (bounce)  {
-               int swmapflags;
+               int swmapflags, plaflags;
 
                /* We always need write access. */
                swmapflags = UVMPAGER_MAPIN_READ;
-               if (!async)
+               plaflags = UVM_PLA_NOWAIT;
+               if (!async) {
                        swmapflags |= UVMPAGER_MAPIN_WAITOK;
-               if (uvm_swap_allocpages(tpps, npages)) {
+                       plaflags = UVM_PLA_WAITOK;
+               }
+               if (uvm_swap_allocpages(tpps, npages, plaflags)) {
                        pool_put(&bufpool, bp);
                        uvm_pagermapout(kva, npages);
                        return (VM_PAGER_AGAIN);