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authorIngo Molnar <mingo@kernel.org>2017-04-23 11:37:17 +0200
committerIngo Molnar <mingo@kernel.org>2017-04-23 11:45:20 +0200
commit6dd29b3df975582ef429b5b93c899e6575785940 (patch)
treef7f214935c45eb7ea9096fccd4cdace3baa99e68 /mm/gup.c
parentace2fb5a8b65d6aba530068ea9331f18e10ef565 (diff)
Revert "x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation"
This reverts commit 2947ba054a4dabbd82848728d765346886050029. Dan Williams reported dax-pmem kernel warnings with the following signature: WARNING: CPU: 8 PID: 245 at lib/percpu-refcount.c:155 percpu_ref_switch_to_atomic_rcu+0x1f5/0x200 percpu ref (dax_pmem_percpu_release [dax_pmem]) <= 0 (0) after switching to atomic ... and bisected it to this commit, which suggests possible memory corruption caused by the x86 fast-GUP conversion. He also pointed out: " This is similar to the backtrace when we were not properly handling pud faults and was fixed with this commit: 220ced1676c4 "mm: fix get_user_pages() vs device-dax pud mappings" I've found some missing _devmap checks in the generic get_user_pages_fast() path, but this does not fix the regression [...] " So given that there are known bugs, and a pretty robust looking bisection points to this commit suggesting that are unknown bugs in the conversion as well, revert it for the time being - we'll re-try in v4.13. Reported-by: Dan Williams <dan.j.williams@intel.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Michal Hocko <mhocko@suse.cz> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: aneesh.kumar@linux.vnet.ibm.com Cc: dann.frazier@canonical.com Cc: dave.hansen@intel.com Cc: steve.capper@linaro.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'mm/gup.c')
-rw-r--r--mm/gup.c10
1 files changed, 5 insertions, 5 deletions
diff --git a/mm/gup.c b/mm/gup.c
index 2559a3987de7..527ec2c6cca3 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1155,7 +1155,7 @@ struct page *get_dump_page(unsigned long addr)
#endif /* CONFIG_ELF_CORE */
/*
- * Generic Fast GUP
+ * Generic RCU Fast GUP
*
* get_user_pages_fast attempts to pin user pages by walking the page
* tables directly and avoids taking locks. Thus the walker needs to be
@@ -1176,8 +1176,8 @@ struct page *get_dump_page(unsigned long addr)
* Before activating this code, please be aware that the following assumptions
* are currently made:
*
- * *) Either HAVE_RCU_TABLE_FREE is enabled, and tlb_remove_table() is used to
- * free pages containing page tables or TLB flushing requires IPI broadcast.
+ * *) HAVE_RCU_TABLE_FREE is enabled, and tlb_remove_table is used to free
+ * pages containing page tables.
*
* *) ptes can be read atomically by the architecture.
*
@@ -1187,7 +1187,7 @@ struct page *get_dump_page(unsigned long addr)
*
* This code is based heavily on the PowerPC implementation by Nick Piggin.
*/
-#ifdef CONFIG_HAVE_GENERIC_GUP
+#ifdef CONFIG_HAVE_GENERIC_RCU_GUP
#ifndef gup_get_pte
/*
@@ -1677,4 +1677,4 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
return ret;
}
-#endif /* CONFIG_HAVE_GENERIC_GUP */
+#endif /* CONFIG_HAVE_GENERIC_RCU_GUP */