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[PATCH] mm: init_mm without ptlock

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First step in pushing down the page_table_lock.  init_mm.page_table_lock has
been used throughout the architectures (usually for ioremap): not to serialize
kernel address space allocation (that's usually vmlist_lock), but because
pud_alloc,pmd_alloc,pte_alloc_kernel expect caller holds it.

Reverse that: don't lock or unlock init_mm.page_table_lock in any of the
architectures; instead rely on pud_alloc,pmd_alloc,pte_alloc_kernel to take
and drop it when allocating a new one, to check lest a racing task already
did.  Similarly no page_table_lock in vmalloc's map_vm_area.

Some temporary ugliness in __pud_alloc and __pmd_alloc: since they also handle
user mms, which are converted only by a later patch, for now they have to lock
differently according to whether or not it's init_mm.

If sources get muddled, there's a danger that an arch source taking
init_mm.page_table_lock will be mixed with common source also taking it (or
neither take it).  So break the rules and make another change, which should
break the build for such a mismatch: remove the redundant mm arg from
pte_alloc_kernel (ppc64 scrapped its distinct ioremap_mm in 2.6.13).

Exceptions: arm26 used pte_alloc_kernel on user mm, now pte_alloc_map; ia64
used pte_alloc_map on init_mm, now pte_alloc_kernel; parisc had bad args to
pmd_alloc and pte_alloc_kernel in unused USE_HPPA_IOREMAP code; ppc64
map_io_page forgot to unlock on failure; ppc mmu_mapin_ram and ppc64 im_free
took page_table_lock for no good reason.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Hugh Dickins
2005-10-29 18:16:21 -07:00
committed by Linus Torvalds
parent 46dea3d092
commit 872fec16d9
26 changed files with 54 additions and 114 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
arch/ppc/mm/pgtable.c
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@@ -280,18 +280,16 @@ map_page(unsigned long va, phys_addr_t pa, int flags)
pte_t *pg;
int err = -ENOMEM;
spin_lock(&init_mm.page_table_lock);
/* Use upper 10 bits of VA to index the first level map */
pd = pmd_offset(pgd_offset_k(va), va);
/* Use middle 10 bits of VA to index the second-level map */
pg = pte_alloc_kernel(&init_mm, pd, va);
pg = pte_alloc_kernel(pd, va);
if (pg != 0) {
err = 0;
set_pte_at(&init_mm, va, pg, pfn_pte(pa >> PAGE_SHIFT, __pgprot(flags)));
if (mem_init_done)
flush_HPTE(0, va, pmd_val(*pd));
}
spin_unlock(&init_mm.page_table_lock);
return err;
}