On Sat, Dec 12, 2020 at 10:54:57PM +1000, Jonathan Matthew wrote: > On Thu, Dec 10, 2020 at 10:46:58AM -0300, Martin Pieuchot wrote: > > 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. > > Right, and as I understand it, kernel threads all share the proc0 vm space, > so its reference count won't ever reach 0, so the kernel map portions of > uvm_unmap_kill_entry() can't be reached from the reaper. Looks like this is > all safe, it just requires a bit more reading than I did the first time. > I'll see if I can find a way to make it more clear.
And now that I've tested this out and checked that it doesn't blow up when you drive the machine into swap, ok jmatthew@ > > > > > 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 */