From 71389703839ebe9cb426c72d5f0bd549592e583c Mon Sep 17 00:00:00 2001 From: Dan Williams Date: Fri, 28 Apr 2017 10:23:37 -0700 Subject: mm, zone_device: Replace {get, put}_zone_device_page() with a single reference to fix pmem crash MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The x86 conversion to the generic GUP code included a small change which causes crashes and data corruption in the pmem code - not good. The root cause is that the /dev/pmem driver code implicitly relies on the x86 get_user_pages() implementation doing a get_page() on the page refcount, because get_page() does a get_zone_device_page() which properly refcounts pmem's separate page struct arrays that are not present in the regular page struct structures. (The pmem driver does this because it can cover huge memory areas.) But the x86 conversion to the generic GUP code changed the get_page() to page_cache_get_speculative() which is faster but doesn't do the get_zone_device_page() call the pmem code relies on. One way to solve the regression would be to change the generic GUP code to use get_page(), but that would slow things down a bit and punish other generic-GUP using architectures for an x86-ism they did not care about. (Arguably the pmem driver was probably not working reliably for them: but nvdimm is an Intel feature, so non-x86 exposure is probably still limited.) So restructure the pmem code's interface with the MM instead: get rid of the get/put_zone_device_page() distinction, integrate put_zone_device_page() into __put_page() and and restructure the pmem completion-wait and teardown machinery: Kirill points out that the calls to {get,put}_dev_pagemap() can be removed from the mm fast path if we take a single get_dev_pagemap() reference to signify that the page is alive and use the final put of the page to drop that reference. This does require some care to make sure that any waits for the percpu_ref to drop to zero occur *after* devm_memremap_page_release(), since it now maintains its own elevated reference. This speeds up things while also making the pmem refcounting more robust going forward. Suggested-by: Kirill Shutemov Tested-by: Kirill Shutemov Signed-off-by: Dan Williams Reviewed-by: Logan Gunthorpe Cc: Andrew Morton Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Jérôme Glisse Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-mm@kvack.org Link: http://lkml.kernel.org/r/149339998297.24933.1129582806028305912.stgit@dwillia2-desk3.amr.corp.intel.com Signed-off-by: Ingo Molnar --- drivers/dax/pmem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers/dax') diff --git a/drivers/dax/pmem.c b/drivers/dax/pmem.c index 033f49b31fdc..cb0d742fa23f 100644 --- a/drivers/dax/pmem.c +++ b/drivers/dax/pmem.c @@ -43,6 +43,7 @@ static void dax_pmem_percpu_exit(void *data) struct dax_pmem *dax_pmem = to_dax_pmem(ref); dev_dbg(dax_pmem->dev, "%s\n", __func__); + wait_for_completion(&dax_pmem->cmp); percpu_ref_exit(ref); } @@ -53,7 +54,6 @@ static void dax_pmem_percpu_kill(void *data) dev_dbg(dax_pmem->dev, "%s\n", __func__); percpu_ref_kill(ref); - wait_for_completion(&dax_pmem->cmp); } static int dax_pmem_probe(struct device *dev) -- cgit v1.2.1