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mm: fix missing wake-up event for FSDAX pages

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FSDAX page refcounts are 1-based, rather than 0-based: if refcount is
1, then the page is freed.  The FSDAX pages can be pinned through GUP,
then they will be unpinned via unpin_user_page() using a folio variant
to put the page, however, folio variants did not consider this special
case, the result will be to miss a wakeup event (like the user of
__fuse_dax_break_layouts()).  This results in a task being permanently
stuck in TASK_INTERRUPTIBLE state.

Since FSDAX pages are only possibly obtained by GUP users, so fix GUP
instead of folio_put() to lower overhead.

Link: https://lkml.kernel.org/r/20220705123532.283-1-songmuchun@bytedance.com
Fixes: d8ddc099c6 ("mm/gup: Add gup_put_folio()")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Suggested-by: Matthew Wilcox <willy@infradead.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Muchun Song 2022-07-05 20:35:32 +08:00 • committed by akpm
parent 3fe2895cfe
commit f4f451a16d
3 changed files with 16 additions and 10 deletions
Download patch file Download diff file Expand all files Collapse all files

6
mm/memremap.c
View file

@ -499,7 +499,7 @@ void free_zone_device_page(struct page *page)
}
#ifdef CONFIG_FS_DAX
bool __put_devmap_managed_page(struct page *page)
bool __put_devmap_managed_page_refs(struct page *page, int refs)
{
if (page->pgmap->type != MEMORY_DEVICE_FS_DAX)
return false;
@ -509,9 +509,9 @@ bool __put_devmap_managed_page(struct page *page)
* refcount is 1, then the page is free and the refcount is
* stable because nobody holds a reference on the page.
*/
if (page_ref_dec_return(page) == 1)
if (page_ref_sub_return(page, refs) == 1)
wake_up_var(&page->_refcount);
return true;
}
EXPORT_SYMBOL(__put_devmap_managed_page);
EXPORT_SYMBOL(__put_devmap_managed_page_refs);
#endif /* CONFIG_FS_DAX */