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futex, thp: remove special case for THP in get_futex_key

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With new THP refcounting, we don't need tricks to stabilize huge page.
If we've got reference to tail page, it can't split under us.

This patch effectively reverts a5b338f2b0 ("thp: update futex compound
knowledge").

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Tested-by: Sasha Levin <sasha.levin@oracle.com>
Tested-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Steve Capper <steve.capper@linaro.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Tested-by: Artem Savkov <artem.savkov@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kirill A. Shutemov 2016-01-15 16:53:00 -08:00 committed by Linus Torvalds
parent ddc58f27f9
commit 14d27abd1d
1 changed files with 14 additions and 49 deletions
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63
kernel/futex.c
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@ -469,7 +469,8 @@ get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
{
unsigned long address = (unsigned long)uaddr;
struct mm_struct *mm = current->mm;
struct page *page, *page_head;
struct page *page;
struct address_space *mapping;
int err, ro = 0;
/*
@ -519,46 +520,9 @@ again:
else
err = 0;
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
page_head = page;
if (unlikely(PageTail(page))) {
put_page(page);
/* serialize against __split_huge_page_splitting() */
local_irq_disable();
if (likely(__get_user_pages_fast(address, 1, !ro, &page) == 1)) {
page_head = compound_head(page);
/*
* page_head is valid pointer but we must pin
* it before taking the PG_lock and/or
* PG_compound_lock. The moment we re-enable
* irqs __split_huge_page_splitting() can
* return and the head page can be freed from
* under us. We can't take the PG_lock and/or
* PG_compound_lock on a page that could be
* freed from under us.
*/
if (page != page_head) {
get_page(page_head);
put_page(page);
}
local_irq_enable();
} else {
local_irq_enable();
goto again;
}
}
#else
page_head = compound_head(page);
if (page != page_head) {
get_page(page_head);
put_page(page);
}
#endif
lock_page(page_head);
lock_page(page);
/*
* If page_head->mapping is NULL, then it cannot be a PageAnon
* If page->mapping is NULL, then it cannot be a PageAnon
* page; but it might be the ZERO_PAGE or in the gate area or
* in a special mapping (all cases which we are happy to fail);
* or it may have been a good file page when get_user_pages_fast
@ -570,12 +534,13 @@ again:
*
* The case we do have to guard against is when memory pressure made
* shmem_writepage move it from filecache to swapcache beneath us:
* an unlikely race, but we do need to retry for page_head->mapping.
* an unlikely race, but we do need to retry for page->mapping.
*/
if (!page_head->mapping) {
int shmem_swizzled = PageSwapCache(page_head);
unlock_page(page_head);
put_page(page_head);
mapping = compound_head(page)->mapping;
if (!mapping) {
int shmem_swizzled = PageSwapCache(page);
unlock_page(page);
put_page(page);
if (shmem_swizzled)
goto again;
return -EFAULT;
@ -588,7 +553,7 @@ again:
* it's a read-only handle, it's expected that futexes attach to
* the object not the particular process.
*/
if (PageAnon(page_head)) {
if (PageAnon(page)) {
/*
* A RO anonymous page will never change and thus doesn't make
* sense for futex operations.
@ -603,15 +568,15 @@ again:
key->private.address = address;
} else {
key->both.offset |= FUT_OFF_INODE; /* inode-based key */
key->shared.inode = page_head->mapping->host;
key->shared.inode = mapping->host;
key->shared.pgoff = basepage_index(page);
}
get_futex_key_refs(key); /* implies MB (B) */
out:
unlock_page(page_head);
put_page(page_head);
unlock_page(page);
put_page(page);
return err;
}