The patch titled
writeback: add debugging code to check time-orderedness of s_dirty
has been added to the -mm tree. Its filename is
check_dirty_inode_list.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: writeback: add debugging code to check time-orderedness of s_dirty
From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
The per-superblock dirty-inode list super_block.s_dirty is supposed to be
sorted in reverse order of each inode's time-of-first-dirtying. This is so
that the kupdate function can avoid having to walk all the dirty inodes on the
list: it terminates the search as soon as it finds an inode which was dirtied
less than 30 seconds ago (dirty_expire_centisecs).
We have a bunch of several-year-old bugs which cause that list to not be in
the correct reverse-time-order. The result of this is that under certain
obscure circumstances, inodes get stuck and basically never get written back.
It has been reported a couple of times, but nobody really cared much because
most people use ordered-mode journalling filesystems, which take care of the
writeback independently. Plus we will _eventually_ get onto these inodes even
when the list is out of order, and a /bin/sync will still work OK.
However this is a pretty important data-integrity issue for filesystems such
as ext2.
As preparation for fixing these bugs, this patch adds a pile of fantastically
expensive debugging code which checks the sanity of the s_dirty list all over
the place, so we find out as soon as it goes bad.
The debugging code is controlled by /proc/sys/fs/inode_debug, which defaults
to off. The debugging will disable itself whenever it detects a misordering,
to avoid log spew.
We can remove all this code later.
Cc: Mike Waychison <mikew@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/fs-writeback.c | 68 +++++++++++++++++++++++++++++++++++-
include/linux/writeback.h | 1
kernel/sysctl.c | 8 ++++
3 files changed, 76 insertions(+), 1 deletion(-)
diff -puN fs/fs-writeback.c~check_dirty_inode_list fs/fs-writeback.c
--- a/fs/fs-writeback.c~check_dirty_inode_list
+++ a/fs/fs-writeback.c
@@ -24,6 +24,49 @@
#include <linux/buffer_head.h>
#include "internal.h"
+int sysctl_inode_debug __read_mostly = 1;
+
+static int __check(struct super_block *sb, int print_stuff)
+{
+ struct list_head *cursor = &sb->s_dirty;
+ unsigned long dirtied_when = 0;
+
+ while ((cursor = cursor->prev) != &sb->s_dirty) {
+ struct inode *inode = list_entry(cursor, struct inode, i_list);
+ if (print_stuff) {
+ printk("%p:%lu\n", inode, inode->dirtied_when);
+ } else {
+ if (dirtied_when &&
+ time_before(inode->dirtied_when, dirtied_when))
+ return 1;
+ dirtied_when = inode->dirtied_when;
+ }
+ }
+ return 0;
+}
+
+static void __check_dirty_inode_list(struct super_block *sb,
+ struct inode *inode, const char *file, int line)
+{
+ if (!sysctl_inode_debug)
+ return;
+
+ if (__check(sb, 0)) {
+ sysctl_inode_debug = 0;
+ if (inode)
+ printk("%s:%d: s_dirty got screwed up. inode=%p:%lu\n",
+ file, line, inode, inode->dirtied_when);
+ else
+ printk("%s:%d: s_dirty got screwed up\n", file, line);
+ __check(sb, 1);
+ }
+}
+
+#define check_dirty_inode_list(sb) \
+ __check_dirty_inode_list(sb, NULL, __FILE__, __LINE__)
+#define check_dirty_inode(inode) \
+ __check_dirty_inode_list(inode->i_sb, inode, __FILE__, __LINE__)
+
/**
* __mark_inode_dirty - internal function
* @inode: inode to mark
@@ -122,8 +165,10 @@ void __mark_inode_dirty(struct inode *in
* reposition it (that would break s_dirty time-ordering).
*/
if (!was_dirty) {
+ check_dirty_inode(inode);
inode->dirtied_when = jiffies;
list_move(&inode->i_list, &sb->s_dirty);
+ check_dirty_inode(inode);
}
}
out:
@@ -200,7 +245,9 @@ __sync_single_inode(struct inode *inode,
* uncongested.
*/
inode->i_state |= I_DIRTY_PAGES;
+ check_dirty_inode(inode);
list_move_tail(&inode->i_list, &sb->s_dirty);
+ check_dirty_inode(inode);
} else {
/*
* Otherwise fully redirty the inode so that
@@ -210,15 +257,19 @@ __sync_single_inode(struct inode *inode,
* all the other files.
*/
inode->i_state |= I_DIRTY_PAGES;
+ check_dirty_inode(inode);
inode->dirtied_when = jiffies;
list_move(&inode->i_list, &sb->s_dirty);
+ check_dirty_inode(inode);
}
} else if (inode->i_state & I_DIRTY) {
/*
* Someone redirtied the inode while were writing back
* the pages.
*/
+ check_dirty_inode(inode);
list_move(&inode->i_list, &sb->s_dirty);
+ check_dirty_inode(inode);
} else if (atomic_read(&inode->i_count)) {
/*
* The inode is clean, inuse
@@ -254,7 +305,9 @@ __writeback_single_inode(struct inode *i
struct address_space *mapping = inode->i_mapping;
int ret;
+ check_dirty_inode(inode);
list_move(&inode->i_list, &inode->i_sb->s_dirty);
+ check_dirty_inode(inode);
/*
* Even if we don't actually write the inode itself here,
@@ -319,8 +372,11 @@ int generic_sync_sb_inodes(struct super_
spin_lock(&inode_lock);
- if (!wbc->for_kupdate || list_empty(&sb->s_io))
+ if (!wbc->for_kupdate || list_empty(&sb->s_io)) {
+ check_dirty_inode_list(sb);
list_splice_init(&sb->s_dirty, &sb->s_io);
+ check_dirty_inode_list(sb);
+ }
while (!list_empty(&sb->s_io)) {
int err;
@@ -332,7 +388,9 @@ int generic_sync_sb_inodes(struct super_
long pages_skipped;
if (!bdi_cap_writeback_dirty(bdi)) {
+ check_dirty_inode(inode);
list_move(&inode->i_list, &sb->s_dirty);
+ check_dirty_inode(inode);
if (sb_is_blkdev_sb(sb)) {
/*
* Dirty memory-backed blockdev: the ramdisk
@@ -352,14 +410,18 @@ int generic_sync_sb_inodes(struct super_
wbc->encountered_congestion = 1;
if (!sb_is_blkdev_sb(sb))
break; /* Skip a congested fs */
+ check_dirty_inode(inode);
list_move(&inode->i_list, &sb->s_dirty);
+ check_dirty_inode(inode);
continue; /* Skip a congested blockdev */
}
if (wbc->bdi && bdi != wbc->bdi) {
if (!sb_is_blkdev_sb(sb))
break; /* fs has the wrong queue */
+ check_dirty_inode(inode);
list_move(&inode->i_list, &sb->s_dirty);
+ check_dirty_inode(inode);
continue; /* blockdev has wrong queue */
}
@@ -383,8 +445,10 @@ int generic_sync_sb_inodes(struct super_
if (!ret)
ret = err;
if (wbc->sync_mode == WB_SYNC_HOLD) {
+ check_dirty_inode(inode);
inode->dirtied_when = jiffies;
list_move(&inode->i_list, &sb->s_dirty);
+ check_dirty_inode(inode);
}
if (current_is_pdflush())
writeback_release(bdi);
@@ -393,7 +457,9 @@ int generic_sync_sb_inodes(struct super_
* writeback is not making progress due to locked
* buffers. Skip this inode for now.
*/
+ check_dirty_inode(inode);
list_move(&inode->i_list, &sb->s_dirty);
+ check_dirty_inode(inode);
}
spin_unlock(&inode_lock);
iput(inode);
diff -puN kernel/sysctl.c~check_dirty_inode_list kernel/sysctl.c
--- a/kernel/sysctl.c~check_dirty_inode_list
+++ a/kernel/sysctl.c
@@ -1079,6 +1079,14 @@ static ctl_table fs_table[] = {
.mode = 0644,
.proc_handler = &proc_dointvec,
},
+ {
+ .ctl_name = CTL_UNNUMBERED,
+ .procname = "inode_debug",
+ .data = &sysctl_inode_debug,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },
#if defined(CONFIG_BINFMT_MISC) || defined(CONFIG_BINFMT_MISC_MODULE)
{
.ctl_name = CTL_UNNUMBERED,
diff -puN include/linux/writeback.h~check_dirty_inode_list include/linux/writeback.h
--- a/include/linux/writeback.h~check_dirty_inode_list
+++ a/include/linux/writeback.h
@@ -132,5 +132,6 @@ void writeback_set_ratelimit(void);
extern int nr_pdflush_threads; /* Global so it can be exported to sysctl
read-only. */
+extern int sysctl_inode_debug;
#endif /* WRITEBACK_H */
_
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check_dirty_inode_list.patch
writeback-fix-time-ordering-of-the-per-superblock-dirty-inode-lists.patch
writeback-fix-time-ordering-of-the-per-superblock-dirty-inode-lists-2.patch
writeback-fix-time-ordering-of-the-per-superblock-dirty-inode-lists-3.patch
writeback-fix-time-ordering-of-the-per-superblock-dirty-inode-lists-4.patch
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