Re: mm: WARNING in __delete_from_page_cache

["Williams, Dan J" <dan.j.williams@intel.com>]

On Mon, 2016-01-25 at 13:22 +0100, Jan Kara wrote:
[..]
> Thanks. Despite the huge list of recipients the author of the changes
> hasn't been CCed :) I've added Dan to CC since he wrote DAX support
> for
> block devices. It seems somehow the write didn't go through the DAX
> path
> but through the standard page cache write path. Ah, I see, only
> file->f_mapping->host has S_DAX set but io_is_direct() which decides
> whether DAX or pagecache path should be used for writes uses file-
> >f_inode
> which is something different for block devices... 

Thanks, yes, the following silences the warning for me:

8<----- (git am --scissors)
Subject: fs, block: force direct-I/O for dax-enabled block devices

From: Dan Williams <dan.j.williams@intel.com>

Similar to the file I/O path, re-direct all I/O to the DAX path for I/O
to a block-device special file.

Otherwise, we confuse the DAX code that does not expect to find live
data in the page cache:

    ------------[ cut here ]------------
    WARNING: CPU: 0 PID: 7676 at mm/filemap.c:217
    __delete_from_page_cache+0x9f6/0xb60()
    Modules linked in:
    CPU: 0 PID: 7676 Comm: a.out Not tainted 4.4.0+ #276
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
     00000000ffffffff ffff88006d3f7738 ffffffff82999e2d 0000000000000000
     ffff8800620a0000 ffffffff86473d20 ffff88006d3f7778 ffffffff81352089
     ffffffff81658d36 ffffffff86473d20 00000000000000d9 ffffea0000009d60
    Call Trace:
     [<     inline     >] __dump_stack lib/dump_stack.c:15
     [<ffffffff82999e2d>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50
     [<ffffffff81352089>] warn_slowpath_common+0xd9/0x140 kernel/panic.c:482
     [<ffffffff813522b9>] warn_slowpath_null+0x29/0x30 kernel/panic.c:515
     [<ffffffff81658d36>] __delete_from_page_cache+0x9f6/0xb60 mm/filemap.c:217
     [<ffffffff81658fb2>] delete_from_page_cache+0x112/0x200 mm/filemap.c:244
     [<ffffffff818af369>] __dax_fault+0x859/0x1800 fs/dax.c:487
     [<ffffffff8186f4f6>] blkdev_dax_fault+0x26/0x30 fs/block_dev.c:1730
     [<     inline     >] wp_pfn_shared mm/memory.c:2208
     [<ffffffff816e9145>] do_wp_page+0xc85/0x14f0 mm/memory.c:2307
     [<     inline     >] handle_pte_fault mm/memory.c:3323
     [<     inline     >] __handle_mm_fault mm/memory.c:3417
     [<ffffffff816ecec3>] handle_mm_fault+0x2483/0x4640 mm/memory.c:3446
     [<ffffffff8127eff6>] __do_page_fault+0x376/0x960 arch/x86/mm/fault.c:1238
     [<ffffffff8127f738>] trace_do_page_fault+0xe8/0x420 arch/x86/mm/fault.c:1331
     [<ffffffff812705c4>] do_async_page_fault+0x14/0xd0 arch/x86/kernel/kvm.c:264
     [<ffffffff86338f78>] async_page_fault+0x28/0x30 arch/x86/entry/entry_64.S:986
     [<ffffffff86336c36>] entry_SYSCALL_64_fastpath+0x16/0x7a
    arch/x86/entry/entry_64.S:185
    ---[ end trace dae21e0f85f1f98c ]---

Cc: Matthew Wilcox <willy@linux.intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Fixes: 5a023cdba50c ("block: enable dax for raw block devices")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Reported-by: Kirill A. Shutemov <kirill@shutemov.name>
Suggested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 fs/block_dev.c     |    5 -----
 include/linux/fs.h |   12 +++++++++++-
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 7b9cd49622b1..277008617b2d 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -156,11 +156,6 @@ blkdev_get_block(struct inode *inode, sector_t iblock,
 	return 0;
 }
 
-static struct inode *bdev_file_inode(struct file *file)
-{
-	return file->f_mapping->host;
-}
-
 static ssize_t
 blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, loff_t offset)
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 1a2046275cdf..a4c4314eed48 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1237,6 +1237,11 @@ static inline struct inode *file_inode(const struct file *f)
 	return f->f_inode;
 }
 
+static inline struct inode *bdev_file_inode(struct file *file)
+{
+	return file->f_mapping->host;
+}
+
 static inline int locks_lock_file_wait(struct file *filp, struct file_lock *fl)
 {
 	return locks_lock_inode_wait(file_inode(filp), fl);
@@ -2907,7 +2912,12 @@ extern void replace_mount_options(struct super_block *sb, char *options);
 
 static inline bool io_is_direct(struct file *filp)
 {
-	return (filp->f_flags & O_DIRECT) || IS_DAX(file_inode(filp));
+	struct inode *inode = file_inode(filp);
+
+	if (S_ISBLK(inode->i_mode))
+		inode = bdev_file_inode(filp);
+
+	return (filp->f_flags & O_DIRECT) || IS_DAX(inode);
 }
 
 static inline int iocb_flags(struct file *file)
--
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