On Mon, Dec 07, 2020 at 03:15:50PM -0300, Martin Pieuchot wrote:
> Getting a page from the fault handler might require poking at some
> swap-related states.
>
> These are not in the hot-path of the fault handler so for the moment
> just assert that the KERNEL_LOCK() is held or grab it if the function
> might be called from an future unlocked path.
>
> ok?
Could you add 'K' to the list of locks in the comment above struct uvmexp too?
I went looking for other uses of swpgonly and saw that it's used under
uvm_map_teardown -> uvm_unmap_kill_entry -> uvm_km_pgremove,
and uvm_map_teardown ensures that the kernel lock is not held.
Not related to this diff exactly, but is this something we need to fix?
>
> Index: uvm/uvm_swap.c
> ===================================================================
> RCS file: /cvs/src/sys/uvm/uvm_swap.c,v
> retrieving revision 1.147
> diff -u -p -r1.147 uvm_swap.c
> --- uvm/uvm_swap.c 29 Sep 2020 11:47:41 -0000 1.147
> +++ uvm/uvm_swap.c 7 Dec 2020 18:07:03 -0000
> @@ -1403,7 +1403,7 @@ uvm_swap_alloc(int *nslots, boolean_t le
> /*
> * lock data lock, convert slots into blocks, and enter loop
> */
> -
> + KERNEL_ASSERT_LOCKED();
> ReTry: /* XXXMRG */
> LIST_FOREACH(spp, &swap_priority, spi_swappri) {
> TAILQ_FOREACH(sdp, &spp->spi_swapdev, swd_next) {
> @@ -1449,8 +1449,10 @@ uvm_swapisfull(void)
> {
> int result;
>
> + KERNEL_LOCK();
> KASSERT(uvmexp.swpgonly <= uvmexp.swpages);
> result = (uvmexp.swpgonly == uvmexp.swpages);
> + KERNEL_UNLOCK();
>
> return result;
> }
> @@ -1465,6 +1467,7 @@ uvm_swap_markbad(int startslot, int nslo
> {
> struct swapdev *sdp;
>
> + KERNEL_LOCK();
> sdp = swapdrum_getsdp(startslot);
> if (sdp != NULL) {
> /*
> @@ -1475,6 +1478,7 @@ uvm_swap_markbad(int startslot, int nslo
> */
> sdp->swd_npgbad += nslots;
> }
> + KERNEL_UNLOCK();
> }
>
> /*
> @@ -1501,7 +1505,7 @@ uvm_swap_free(int startslot, int nslots)
> * in the extent, and return. must hold pri lock to do
> * lookup and access the extent.
> */
> -
> + KERNEL_LOCK();
> sdp = swapdrum_getsdp(startslot);
> KASSERT(uvmexp.nswapdev >= 1);
> KASSERT(sdp != NULL);
> @@ -1533,6 +1537,7 @@ uvm_swap_free(int startslot, int nslots)
> }
> }
> #endif /* UVM_SWAP_ENCRYPT */
> + KERNEL_UNLOCK();
> }
>
> /*
> @@ -1567,6 +1572,7 @@ uvm_swap_get(struct vm_page *page, int s
> return VM_PAGER_ERROR;
> }
>
> + KERNEL_LOCK();
> /* this page is (about to be) no longer only in swap. */
> uvmexp.swpgonly--;
>
> @@ -1577,7 +1583,7 @@ uvm_swap_get(struct vm_page *page, int s
> /* oops, the read failed so it really is still only in swap. */
> uvmexp.swpgonly++;
> }
> -
> + KERNEL_UNLOCK();
> return (result);
> }
>
> @@ -1599,6 +1605,8 @@ uvm_swap_io(struct vm_page **pps, int st
> struct swapdev *sdp;
> int encrypt = 0;
> #endif
> +
> + KERNEL_ASSERT_LOCKED();
>
> write = (flags & B_READ) == 0;
> async = (flags & B_ASYNC) != 0;
> Index: uvm/uvmexp.h
> ===================================================================
> RCS file: /cvs/src/sys/uvm/uvmexp.h,v
> retrieving revision 1.6
> diff -u -p -r1.6 uvmexp.h
> --- uvm/uvmexp.h 1 Dec 2020 13:56:22 -0000 1.6
> +++ uvm/uvmexp.h 7 Dec 2020 18:09:06 -0000
> @@ -79,9 +79,9 @@ struct uvmexp {
>
> /* swap */
> int nswapdev; /* number of configured swap devices in system */
> - int swpages; /* number of PAGE_SIZE'ed swap pages */
> + int swpages; /* [K] number of PAGE_SIZE'ed swap pages */
> int swpginuse; /* number of swap pages in use */
> - int swpgonly; /* number of swap pages in use, not also in RAM */
> + int swpgonly; /* [K] number of swap pages in use, not also in RAM */
> int nswget; /* number of swap pages moved from disk to RAM */
> int nanon; /* XXX number total of anon's in system */
> int unused05; /* formerly nanonneeded */
>
