On 08/12/20(Tue) 22:55, Jonathan Matthew wrote:
> 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?
Updated diff below.
> 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?
I suppose that the problem can only occur if a kernel thread is exiting
since this code is only executed for the kernel pmap. Anyway I added an
assertion.
Index: uvm/uvm_km.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_km.c,v
retrieving revision 1.137
diff -u -p -r1.137 uvm_km.c
--- uvm/uvm_km.c 23 May 2020 06:15:09 -0000 1.137
+++ uvm/uvm_km.c 10 Dec 2020 13:33:49 -0000
@@ -243,6 +243,7 @@ uvm_km_pgremove(struct uvm_object *uobj,
voff_t curoff;
int slot;
+ KERNEL_ASSERT_LOCKED();
KASSERT(uobj->pgops == &aobj_pager);
for (curoff = start ; curoff < end ; curoff += PAGE_SIZE) {
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 10 Dec 2020 13:30:30 -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 10 Dec 2020 13:31:01 -0000
@@ -42,6 +42,7 @@
*
* Locks used to protect struct members in this file:
* I immutable after creation
+ * K kernel lock
* F uvm_lock_fpageq
*/
struct uvmexp {
@@ -79,9 +80,9 @@ 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 */
