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From: Miklos Szeredi <mszeredi@redhat.com>
To: linux-unionfs@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 26/39] ovl: copy-up on MAP_SHARED
Date: Tue, 29 May 2018 16:43:26 +0200	[thread overview]
Message-ID: <20180529144339.16538-27-mszeredi@redhat.com> (raw)
In-Reply-To: <20180529144339.16538-1-mszeredi@redhat.com>

A corner case of a corner case is when

 - file opened for O_RDONLY
 - which is then memory mapped SHARED
 - file opened for O_WRONLY
 - contents modified
 - contents read back though the shared mapping

Unfortunately it looks very difficult to do anything about the established
shared map after the file is copied up.

Instead, when a read-only file is mapped shared, copy up the file before
actually doing the map.  This may result in unnecessary copy-ups (but so
may copy-up on open(O_RDWR) for exampe).

We can revisit this later if it turns out to be a performance problem in
real life.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/Kconfig     | 21 +++++++++++++++++++++
 fs/overlayfs/file.c      | 22 ++++++++++++++++++++++
 fs/overlayfs/overlayfs.h |  7 +++++++
 fs/overlayfs/ovl_entry.h |  1 +
 fs/overlayfs/super.c     | 22 ++++++++++++++++++++++
 5 files changed, 73 insertions(+)

diff --git a/fs/overlayfs/Kconfig b/fs/overlayfs/Kconfig
index 17032631c5cf..5d1d40d745c5 100644
--- a/fs/overlayfs/Kconfig
+++ b/fs/overlayfs/Kconfig
@@ -103,3 +103,24 @@ config OVERLAY_FS_XINO_AUTO
 	  For more information, see Documentation/filesystems/overlayfs.txt
 
 	  If unsure, say N.
+
+config OVERLAY_FS_COPY_UP_SHARED
+	bool "Overlayfs: copy up when mapping a file shared"
+	default n
+	depends on OVERLAY_FS
+	help
+	  If this option is enabled then on mapping a file with MAP_SHARED
+	  overlayfs copies up the file in anticipation of it being modified
+	  (just like we copy up the file on O_WRONLY and O_RDWR in anticipation
+	  of modification).  This does not interfere with shared library
+	  loading, as that uses MAP_PRIVATE.  But there might be use cases out
+	  there where this impacts performance and disk usage.
+
+	  This just selects the default, the feature can also be enabled or
+	  disabled in the running kernel or individually on each overlay mount.
+
+	  To get maximally standard compliant behavior, enable this option.
+
+	  To get a maximally backward compatible kernel, disable this option.
+
+	  If unsure, say N.
diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index ef4bcc80572f..266692ce9a9a 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -10,6 +10,7 @@
 #include <linux/file.h>
 #include <linux/mount.h>
 #include <linux/xattr.h>
+#include <linux/mman.h>
 #include <linux/uio.h>
 #include "overlayfs.h"
 
@@ -259,6 +260,26 @@ static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 	return ret;
 }
 
+static int ovl_pre_mmap(struct file *file, unsigned long prot,
+			unsigned long flag)
+{
+	int err = 0;
+
+	/*
+	 * Take MAP_SHARED as hint about future writes to the file (through
+	 * another file descriptor).  Caller might not have had such an intent,
+	 * but we hope MAP_PRIVATE will be used in most such cases.
+	 *
+	 * If we don't copy up now and the file is modified, it becomes really
+	 * difficult to change the mapping to match that of the file's content
+	 * later.
+	 */
+	if ((flag & MAP_SHARED) && ovl_copy_up_shared(file_inode(file)->i_sb))
+		err = ovl_copy_up(file_dentry(file));
+
+	return err;
+}
+
 static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
 {
 	struct fd real;
@@ -476,6 +497,7 @@ const struct file_operations ovl_file_operations = {
 	.read_iter	= ovl_read_iter,
 	.write_iter	= ovl_write_iter,
 	.fsync		= ovl_fsync,
+	.pre_mmap	= ovl_pre_mmap,
 	.mmap		= ovl_mmap,
 	.fallocate	= ovl_fallocate,
 	.unlocked_ioctl	= ovl_ioctl,
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 3f6e39a2f51e..be4f1664f662 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -266,6 +266,13 @@ static inline unsigned int ovl_xino_bits(struct super_block *sb)
 	return ofs->xino_bits;
 }
 
+static inline bool ovl_copy_up_shared(struct super_block *sb)
+{
+	struct ovl_fs *ofs = sb->s_fs_info;
+
+	return !(sb->s_flags & SB_RDONLY) && ofs->config.copy_up_shared;
+}
+
 
 /* namei.c */
 int ovl_check_fh_len(struct ovl_fh *fh, int fh_len);
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index 41655a7d6894..3bea47c63fd9 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -18,6 +18,7 @@ struct ovl_config {
 	const char *redirect_mode;
 	bool index;
 	bool nfs_export;
+	bool copy_up_shared;
 	int xino;
 };
 
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 211975921a90..900ed4c39919 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -56,6 +56,12 @@ module_param_named(xino_auto, ovl_xino_auto_def, bool, 0644);
 MODULE_PARM_DESC(ovl_xino_auto_def,
 		 "Auto enable xino feature");
 
+static bool ovl_copy_up_shared_def =
+	IS_ENABLED(CONFIG_OVERLAY_FS_COPY_UP_SHARED);
+module_param_named(copy_up_shared, ovl_copy_up_shared_def, bool, 0644);
+MODULE_PARM_DESC(ovl_copy_up_shared_def,
+		 "Copy up when mapping a file shared");
+
 static void ovl_entry_stack_free(struct ovl_entry *oe)
 {
 	unsigned int i;
@@ -380,6 +386,9 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
 						"on" : "off");
 	if (ofs->config.xino != ovl_xino_def())
 		seq_printf(m, ",xino=%s", ovl_xino_str[ofs->config.xino]);
+	if (ofs->config.copy_up_shared != ovl_copy_up_shared_def)
+		seq_printf(m, ",copy_up_shared=%s",
+			   ofs->config.copy_up_shared ? "on" : "off");
 	return 0;
 }
 
@@ -417,6 +426,8 @@ enum {
 	OPT_XINO_ON,
 	OPT_XINO_OFF,
 	OPT_XINO_AUTO,
+	OPT_COPY_UP_SHARED_ON,
+	OPT_COPY_UP_SHARED_OFF,
 	OPT_ERR,
 };
 
@@ -433,6 +444,8 @@ static const match_table_t ovl_tokens = {
 	{OPT_XINO_ON,			"xino=on"},
 	{OPT_XINO_OFF,			"xino=off"},
 	{OPT_XINO_AUTO,			"xino=auto"},
+	{OPT_COPY_UP_SHARED_ON,		"copy_up_shared=on"},
+	{OPT_COPY_UP_SHARED_OFF,	"copy_up_shared=off"},
 	{OPT_ERR,			NULL}
 };
 
@@ -559,6 +572,14 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
 			config->xino = OVL_XINO_AUTO;
 			break;
 
+		case OPT_COPY_UP_SHARED_ON:
+			config->copy_up_shared = true;
+			break;
+
+		case OPT_COPY_UP_SHARED_OFF:
+			config->copy_up_shared = false;
+			break;
+
 		default:
 			pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
 			return -EINVAL;
@@ -1379,6 +1400,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	ofs->config.index = ovl_index_def;
 	ofs->config.nfs_export = ovl_nfs_export_def;
 	ofs->config.xino = ovl_xino_def();
+	ofs->config.copy_up_shared = ovl_copy_up_shared_def;
 	err = ovl_parse_opt((char *) data, &ofs->config);
 	if (err)
 		goto out_err;
-- 
2.14.3

  parent reply	other threads:[~2018-05-29 14:44 UTC|newest]

Thread overview: 83+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-29 14:43 [PATCH 00/39] overlayfs: stack file operations Miklos Szeredi
2018-05-29 14:43 ` [PATCH 01/39] vfs: dedpue: return loff_t Miklos Szeredi
2018-06-04  8:43   ` Christoph Hellwig
2018-06-05  8:33     ` Miklos Szeredi
2018-06-06 15:09       ` Darrick J. Wong
2018-06-18 20:08         ` Miklos Szeredi
2018-05-29 14:43 ` [PATCH 02/39] vfs: dedupe: rationalize args Miklos Szeredi
2018-06-06 15:02   ` Darrick J. Wong
2018-05-29 14:43 ` [PATCH 03/39] vfs: dedupe: extract helper for a single dedup Miklos Szeredi
2018-05-29 15:41   ` Amir Goldstein
2018-05-29 16:04     ` Amir Goldstein
2018-06-04  8:44   ` Christoph Hellwig
2018-05-29 14:43 ` [PATCH 04/39] vfs: add path_open() Miklos Szeredi
2018-06-04  8:46   ` Christoph Hellwig
2018-06-10  4:36     ` Al Viro
2018-05-29 14:43 ` [PATCH 05/39] vfs: optionally don't account file in nr_files Miklos Szeredi
2018-06-04  8:47   ` Christoph Hellwig
2018-06-04  8:57     ` Miklos Szeredi
2018-06-10  4:41   ` Al Viro
2018-05-29 14:43 ` [PATCH 06/39] vfs: add f_op->pre_mmap() Miklos Szeredi
2018-06-04  8:48   ` Christoph Hellwig
2018-06-05 11:36     ` Miklos Szeredi
2018-05-29 14:43 ` [PATCH 07/39] vfs: export vfs_ioctl() to modules Miklos Szeredi
2018-06-04  8:49   ` Christoph Hellwig
2018-06-10  4:57     ` Al Viro
2018-06-11  7:19       ` Miklos Szeredi
2018-06-11 16:24         ` Christoph Hellwig
2018-06-19 14:04           ` Miklos Szeredi
2018-06-19 14:24             ` Christoph Hellwig
2018-06-19 14:34               ` Miklos Szeredi
2018-06-19 14:54                 ` Al Viro
2018-05-29 14:43 ` [PATCH 08/39] vfs: export vfs_dedupe_file_range_one() " Miklos Szeredi
2018-05-29 14:43 ` [PATCH 09/39] ovl: copy up times Miklos Szeredi
2018-05-29 14:43 ` [PATCH 10/39] ovl: copy up inode flags Miklos Szeredi
2018-05-29 14:43 ` [PATCH 11/39] Revert "Revert "ovl: get_write_access() in truncate"" Miklos Szeredi
2018-05-29 14:43 ` [PATCH 12/39] ovl: copy up file size as well Miklos Szeredi
2018-05-29 14:43 ` [PATCH 13/39] ovl: deal with overlay files in ovl_d_real() Miklos Szeredi
2018-05-29 14:43 ` [PATCH 14/39] ovl: stack file ops Miklos Szeredi
2018-06-10  4:13   ` Al Viro
2018-06-11  7:09     ` Miklos Szeredi
2018-06-12  2:29       ` Al Viro
2018-06-12  2:40         ` Al Viro
2018-06-12  9:24           ` Miklos Szeredi
2018-06-12 18:24             ` Al Viro
2018-06-12 18:31               ` Al Viro
2018-06-13  9:21                 ` Miklos Szeredi
2018-06-15  5:47                   ` Al Viro
2018-06-18 11:50                     ` Miklos Szeredi
2018-06-13 11:56               ` J. R. Okajima
2018-05-29 14:43 ` [PATCH 15/39] ovl: add helper to return real file Miklos Szeredi
2018-06-10  5:42   ` Al Viro
2018-06-11  8:11     ` Miklos Szeredi
2018-05-29 14:43 ` [PATCH 16/39] ovl: add ovl_read_iter() Miklos Szeredi
2018-05-29 14:43 ` [PATCH 17/39] ovl: add ovl_write_iter() Miklos Szeredi
2018-05-29 14:43 ` [PATCH 18/39] ovl: add ovl_fsync() Miklos Szeredi
2018-05-29 14:43 ` [PATCH 19/39] ovl: add ovl_mmap() Miklos Szeredi
2018-06-10  5:24   ` Al Viro
2018-06-11  7:58     ` Miklos Szeredi
2018-05-29 14:43 ` [PATCH 20/39] ovl: add ovl_fallocate() Miklos Szeredi
2018-05-29 14:43 ` [PATCH 21/39] ovl: add lsattr/chattr support Miklos Szeredi
2018-05-29 14:43 ` [PATCH 22/39] ovl: add ovl_fiemap() Miklos Szeredi
2018-05-29 14:43 ` [PATCH 23/39] ovl: add O_DIRECT support Miklos Szeredi
2018-06-10  5:31   ` Al Viro
2018-06-11  8:08     ` Miklos Szeredi
2018-05-29 14:43 ` [PATCH 24/39] ovl: add reflink/copyfile/dedup support Miklos Szeredi
2018-05-29 14:43 ` [PATCH 25/39] vfs: don't open real Miklos Szeredi
2018-05-29 14:43 ` Miklos Szeredi [this message]
2018-05-29 14:43 ` [PATCH 27/39] ovl: obsolete "check_copy_up" module option Miklos Szeredi
2018-05-29 15:13   ` Amir Goldstein
2018-05-30  8:26     ` Miklos Szeredi
2018-05-29 14:43 ` [PATCH 28/39] ovl: fix documentation of non-standard behavior Miklos Szeredi
2018-05-29 14:43 ` [PATCH 29/39] vfs: simplify dentry_open() Miklos Szeredi
2018-05-29 14:43 ` [PATCH 30/39] Revert "ovl: fix may_write_real() for overlayfs directories" Miklos Szeredi
2018-05-29 14:43 ` [PATCH 31/39] Revert "ovl: don't allow writing ioctl on lower layer" Miklos Szeredi
2018-05-29 14:43 ` [PATCH 32/39] vfs: fix freeze protection in mnt_want_write_file() for overlayfs Miklos Szeredi
2018-06-04  8:50   ` Christoph Hellwig
2018-05-29 14:43 ` [PATCH 33/39] Revert "ovl: fix relatime for directories" Miklos Szeredi
2018-05-29 14:43 ` [PATCH 34/39] Revert "vfs: update ovl inode before relatime check" Miklos Szeredi
2018-05-29 14:43 ` [PATCH 35/39] Revert "vfs: add flags to d_real()" Miklos Szeredi
2018-05-29 14:43 ` [PATCH 36/39] Revert "vfs: do get_write_access() on upper layer of overlayfs" Miklos Szeredi
2018-05-29 14:43 ` [PATCH 37/39] Partially revert "locks: fix file locking on overlayfs" Miklos Szeredi
2018-05-29 14:43 ` [PATCH 38/39] Revert "fsnotify: support overlayfs" Miklos Szeredi
2018-05-29 14:43 ` [PATCH 39/39] vfs: remove open_flags from d_real() Miklos Szeredi

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