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Correct the handling of two unusual cases by the zero-copy receive path,

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specifically, vm_pgmoveco():
1. If vm_pgmoveco() sleeps on a busy page, it must redo the look up
because the page may have been freed.
2. If the receive buffer is copy-on-write due to, for example, a fork,
then although the first vm object in the shadow chain may not contain
a page there may still be one from a backing object that is mapped.
Thus, a pmap_remove() is required for the new page rather than the
backing object's page to been seen by the application.

Also, add some comments to vm_pgmoveco() and update some assertions.

Tested by: ken@
This commit is contained in:
Alan Cox 2004-12-13 06:24:14 +00:00
parent 98a67cd840
commit db24060c25
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=138781
1 changed files with 26 additions and 16 deletions
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42
sys/kern/kern_subr.c
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@ -68,6 +68,12 @@ SYSCTL_INT(_kern, KERN_IOV_MAX, iov_max, CTLFLAG_RD, NULL, UIO_MAXIOV,
/* Declared in uipc_socket.c */
extern int so_zero_copy_receive;
/*
* Identify the physical page mapped at the given kernel virtual
* address. Insert this physical page into the given address space at
* the given virtual address, replacing the physical page, if any,
* that already exists there.
*/
static int
vm_pgmoveco(vm_map_t mapa, vm_offset_t kaddr, vm_offset_t uaddr)
{
@ -79,10 +85,17 @@ vm_pgmoveco(vm_map_t mapa, vm_offset_t kaddr, vm_offset_t uaddr)
vm_prot_t prot;
boolean_t wired;
KASSERT((uaddr & PAGE_MASK) == 0,
("vm_pgmoveco: uaddr is not page aligned"));
/*
* First lookup the kernel page.
* Herein the physical page is validated and dirtied. It is
* unwired in sf_buf_mext().
*/
kern_pg = PHYS_TO_VM_PAGE(vtophys(kaddr));
kern_pg->valid = VM_PAGE_BITS_ALL;
KASSERT(kern_pg->queue == PQ_NONE && kern_pg->wire_count == 1,
("vm_pgmoveco: kern_pg is not correctly wired"));
if ((vm_map_lookup(&map, uaddr,
VM_PROT_WRITE, &entry, &uobject,
@ -90,28 +103,25 @@ vm_pgmoveco(vm_map_t mapa, vm_offset_t kaddr, vm_offset_t uaddr)
return(EFAULT);
}
VM_OBJECT_LOCK(uobject);
retry:
if ((user_pg = vm_page_lookup(uobject, upindex)) != NULL) {
do
vm_page_lock_queues();
while (vm_page_sleep_if_busy(user_pg, 1, "vm_pgmoveco"));
vm_page_lock_queues();
if (vm_page_sleep_if_busy(user_pg, 1, "vm_pgmoveco"))
goto retry;
pmap_remove_all(user_pg);
vm_page_free(user_pg);
} else
} else {
/*
* Even if a physical page does not exist in the
* object chain's first object, a physical page from a
* backing object may be mapped read only.
*/
if (uobject->backing_object != NULL)
pmap_remove(map->pmap, uaddr, uaddr + PAGE_SIZE);
vm_page_lock_queues();
if (kern_pg->busy || ((kern_pg->queue - kern_pg->pc) == PQ_FREE) ||
(kern_pg->hold_count != 0)|| (kern_pg->flags & PG_BUSY)) {
printf("vm_pgmoveco: pindex(%lu), busy(%d), PG_BUSY(%d), "
"hold(%d) paddr(0x%lx)\n", (u_long)kern_pg->pindex,
kern_pg->busy, (kern_pg->flags & PG_BUSY) ? 1 : 0,
kern_pg->hold_count, (u_long)kern_pg->phys_addr);
if ((kern_pg->queue - kern_pg->pc) == PQ_FREE)
panic("vm_pgmoveco: renaming free page");
else
panic("vm_pgmoveco: renaming busy page");
}
vm_page_insert(kern_pg, uobject, upindex);
vm_page_dirty(kern_pg);
kern_pg->valid = VM_PAGE_BITS_ALL;
vm_page_unlock_queues();
VM_OBJECT_UNLOCK(uobject);
vm_map_lookup_done(map, entry);