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mm/gup: combine put_compound_head() and unpin_user_page()

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These functions accomplish the same thing but have different
implementations.

unpin_user_page() has a bug where it calls mod_node_page_state() after
calling put_page() which creates a risk that the page could have been
hot-uplugged from the system.

Fix this by using put_compound_head() as the only implementation.

__unpin_devmap_managed_user_page() and related can be deleted as well in
favour of the simpler, but slower, version in put_compound_head() that has
an extra atomic page_ref_sub, but always calls put_page() which internally
contains the special devmap code.

Move put_compound_head() to be directly after try_grab_compound_head() so
people can find it in future.

Link: https://lkml.kernel.org/r/0-v1-6730d4ee0d32+40e6-gup_combine_put_jgg@nvidia.com
Fixes: 1970dc6f52 ("mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN) reporting")
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
CC: Joao Martins <joao.m.martins@oracle.com>
CC: Jonathan Corbet <corbet@lwn.net>
CC: Dan Williams <dan.j.williams@intel.com>
CC: Dave Chinner <david@fromorbit.com>
CC: Christoph Hellwig <hch@infradead.org>
CC: Jane Chu <jane.chu@oracle.com>
CC: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
CC: Michal Hocko <mhocko@suse.com>
CC: Mike Kravetz <mike.kravetz@oracle.com>
CC: Shuah Khan <shuah@kernel.org>
CC: Muchun Song <songmuchun@bytedance.com>
CC: Vlastimil Babka <vbabka@suse.cz>
CC: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jason Gunthorpe 2020-12-14 19:05:51 -08:00 committed by Linus Torvalds
parent 52650c8b46
commit 4509b42c38
1 changed files with 23 additions and 80 deletions
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103
mm/gup.c
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@ -123,6 +123,28 @@ static __maybe_unused struct page *try_grab_compound_head(struct page *page,
return NULL;
}
static void put_compound_head(struct page *page, int refs, unsigned int flags)
{
if (flags & FOLL_PIN) {
mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED,
refs);
if (hpage_pincount_available(page))
hpage_pincount_sub(page, refs);
else
refs *= GUP_PIN_COUNTING_BIAS;
}
VM_BUG_ON_PAGE(page_ref_count(page) < refs, page);
/*
* Calling put_page() for each ref is unnecessarily slow. Only the last
* ref needs a put_page().
*/
if (refs > 1)
page_ref_sub(page, refs - 1);
put_page(page);
}
/**
* try_grab_page() - elevate a page's refcount by a flag-dependent amount
*
@ -177,41 +199,6 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags)
return true;
}
#ifdef CONFIG_DEV_PAGEMAP_OPS
static bool __unpin_devmap_managed_user_page(struct page *page)
{
int count, refs = 1;
if (!page_is_devmap_managed(page))
return false;
if (hpage_pincount_available(page))
hpage_pincount_sub(page, 1);
else
refs = GUP_PIN_COUNTING_BIAS;
count = page_ref_sub_return(page, refs);
mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, 1);
/*
* devmap page refcounts are 1-based, rather than 0-based: if
* refcount is 1, then the page is free and the refcount is
* stable because nobody holds a reference on the page.
*/
if (count == 1)
free_devmap_managed_page(page);
else if (!count)
__put_page(page);
return true;
}
#else
static bool __unpin_devmap_managed_user_page(struct page *page)
{
return false;
}
#endif /* CONFIG_DEV_PAGEMAP_OPS */
/**
* unpin_user_page() - release a dma-pinned page
* @page: pointer to page to be released
@ -223,28 +210,7 @@ static bool __unpin_devmap_managed_user_page(struct page *page)
*/
void unpin_user_page(struct page *page)
{
int refs = 1;
page = compound_head(page);
/*
* For devmap managed pages we need to catch refcount transition from
* GUP_PIN_COUNTING_BIAS to 1, when refcount reach one it means the
* page is free and we need to inform the device driver through
* callback. See include/linux/memremap.h and HMM for details.
*/
if (__unpin_devmap_managed_user_page(page))
return;
if (hpage_pincount_available(page))
hpage_pincount_sub(page, 1);
else
refs = GUP_PIN_COUNTING_BIAS;
if (page_ref_sub_and_test(page, refs))
__put_page(page);
mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, 1);
put_compound_head(compound_head(page), 1, FOLL_PIN);
}
EXPORT_SYMBOL(unpin_user_page);
@ -2009,29 +1975,6 @@ EXPORT_SYMBOL(get_user_pages_unlocked);
* This code is based heavily on the PowerPC implementation by Nick Piggin.
*/
#ifdef CONFIG_HAVE_FAST_GUP
static void put_compound_head(struct page *page, int refs, unsigned int flags)
{
if (flags & FOLL_PIN) {
mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED,
refs);
if (hpage_pincount_available(page))
hpage_pincount_sub(page, refs);
else
refs *= GUP_PIN_COUNTING_BIAS;
}
VM_BUG_ON_PAGE(page_ref_count(page) < refs, page);
/*
* Calling put_page() for each ref is unnecessarily slow. Only the last
* ref needs a put_page().
*/
if (refs > 1)
page_ref_sub(page, refs - 1);
put_page(page);
}
#ifdef CONFIG_GUP_GET_PTE_LOW_HIGH
/*