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Revert "mm/gup: small refactoring: simplify try_grab_page()" 

This reverts commit 54d516b1d6

That commit did a refactoring that effectively combined fast and slow
gup paths (again).  And that was again incorrect, for two reasons:

 a) Fast gup and slow gup get reference counts on pages in different
    ways and with different goals: see Linus' writeup in commit
    cd1adf1b63 ("Revert "mm/gup: remove try_get_page(), call
    try_get_compound_head() directly""), and

 b) try_grab_compound_head() also has a specific check for
    "FOLL_LONGTERM && !is_pinned(page)", that assumes that the caller
    can fall back to slow gup. This resulted in new failures, as
    recently report by Will McVicker [1].

But (a) has problems too, even though they may not have been reported
yet.  So just revert this.

Link: https://lore.kernel.org/r/20220131203504.3458775-1-willmcvicker@google.com [1]
Fixes: 54d516b1d6 ("mm/gup: small refactoring: simplify try_grab_page()")
Reported-and-tested-by: Will McVicker <willmcvicker@google.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Minchan Kim <minchan@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: stable@vger.kernel.org # 5.15
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
John Hubbard 2022-02-01 19:23:17 -08:00 committed by Linus Torvalds
parent d394bb77dd
commit c36c04c2e1
1 changed files with 30 additions and 5 deletions
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35
mm/gup.c
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@ -124,8 +124,8 @@ static inline struct page *try_get_compound_head(struct page *page, int refs)
* considered failure, and furthermore, a likely bug in the caller, so a warning
* is also emitted.
*/
struct page *try_grab_compound_head(struct page *page,
int refs, unsigned int flags)
__maybe_unused struct page *try_grab_compound_head(struct page *page,
int refs, unsigned int flags)
{
if (flags & FOLL_GET)
return try_get_compound_head(page, refs);
@ -208,10 +208,35 @@ static void put_compound_head(struct page *page, int refs, unsigned int flags)
*/
bool __must_check try_grab_page(struct page *page, unsigned int flags)
{
if (!(flags & (FOLL_GET | FOLL_PIN)))
return true;
WARN_ON_ONCE((flags & (FOLL_GET | FOLL_PIN)) == (FOLL_GET | FOLL_PIN));
return try_grab_compound_head(page, 1, flags);
if (flags & FOLL_GET)
return try_get_page(page);
else if (flags & FOLL_PIN) {
int refs = 1;
page = compound_head(page);
if (WARN_ON_ONCE(page_ref_count(page) <= 0))
return false;
if (hpage_pincount_available(page))
hpage_pincount_add(page, 1);
else
refs = GUP_PIN_COUNTING_BIAS;
/*
* Similar to try_grab_compound_head(): even if using the
* hpage_pincount_add/_sub() routines, be sure to
* *also* increment the normal page refcount field at least
* once, so that the page really is pinned.
*/
page_ref_add(page, refs);
mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_ACQUIRED, 1);
}
return true;
}
/**