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authorDan Williams <dan.j.williams@intel.com>2015-11-15 16:06:32 -0800
committerDan Williams <dan.j.williams@intel.com>2015-11-16 23:54:45 -0800
commitee82c9ed41e896bd47e121d87e4628de0f2656a3 (patch)
tree2f1b320de88531e2c614c74f0fbc0fa7f50e0ad8 /fs
parentef83b6e8f40bb24b92ad73b5889732346e54a793 (diff)
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dax: disable pmd mappings
While dax pmd mappings are functional in the nominal path they trigger kernel crashes in the following paths: BUG: unable to handle kernel paging request at ffffea0004098000 IP: [<ffffffff812362f7>] follow_trans_huge_pmd+0x117/0x3b0 [..] Call Trace: [<ffffffff811f6573>] follow_page_mask+0x2d3/0x380 [<ffffffff811f6708>] __get_user_pages+0xe8/0x6f0 [<ffffffff811f7045>] get_user_pages_unlocked+0x165/0x1e0 [<ffffffff8106f5b1>] get_user_pages_fast+0xa1/0x1b0 kernel BUG at arch/x86/mm/gup.c:131! [..] Call Trace: [<ffffffff8106f34c>] gup_pud_range+0x1bc/0x220 [<ffffffff8106f634>] get_user_pages_fast+0x124/0x1b0 BUG: unable to handle kernel paging request at ffffea0004088000 IP: [<ffffffff81235f49>] copy_huge_pmd+0x159/0x350 [..] Call Trace: [<ffffffff811fad3c>] copy_page_range+0x34c/0x9f0 [<ffffffff810a0daf>] copy_process+0x1b7f/0x1e10 [<ffffffff810a11c1>] _do_fork+0x91/0x590 All of these paths are interpreting a dax pmd mapping as a transparent huge page and making the assumption that the pfn is covered by the memmap, i.e. that the pfn has an associated struct page. PTE mappings do not suffer the same fate since they have the _PAGE_SPECIAL flag to cause the gup path to fault. We can do something similar for the PMD path, or otherwise defer pmd support for cases where a struct page is available. For now, 4.4-rc and -stable need to disable dax pmd support by default. For development the "depends on BROKEN" line can be removed from CONFIG_FS_DAX_PMD. Cc: <stable@vger.kernel.org> Cc: Jan Kara <jack@suse.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Matthew Wilcox <willy@linux.intel.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reported-by: Ross Zwisler <ross.zwisler@linux.intel.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Diffstat (limited to 'fs')
-rw-r--r--fs/Kconfig6
-rw-r--r--fs/dax.c4
2 files changed, 10 insertions, 0 deletions
diff --git a/fs/Kconfig b/fs/Kconfig
index da3f32f..6ce72d8 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -46,6 +46,12 @@ config FS_DAX
or if unsure, say N. Saying Y will increase the size of the kernel
by about 5kB.
+config FS_DAX_PMD
+ bool
+ default FS_DAX
+ depends on FS_DAX
+ depends on BROKEN
+
endif # BLOCK
# Posix ACL utility routines
diff --git a/fs/dax.c b/fs/dax.c
index d1e5cb7..43671b6 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -541,6 +541,10 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
unsigned long pfn;
int result = 0;
+ /* dax pmd mappings are broken wrt gup and fork */
+ if (!IS_ENABLED(CONFIG_FS_DAX_PMD))
+ return VM_FAULT_FALLBACK;
+
/* Fall back to PTEs if we're going to COW */
if (write && !(vma->vm_flags & VM_SHARED))
return VM_FAULT_FALLBACK;
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