On Wed, 16 May 2007 10:15:35 -0700, Andrew Morton wrote:
>
> If we're going to do this then please let's get some exhaustive commentary
> in there so that others have a chance of understanding these flags without
> having to do the amount of reverse-engineering which you've been put through.
Done. Found and fixed some bugs in the process. By now I feal
reasonable certain that the patch fixes more than it breaks.
Jörn
--
Good warriors cause others to come to them and do not go to others.
-- Sun Tzu
Introduce I_SYNC.
I_LOCK was used for several unrelated purposes, which caused deadlock
situations in certain filesystems as a side effect. One of the purposes
now uses the new I_SYNC bit.
Also document the various bits and change their order from historical to
logical.
Signed-off-by: Jörn Engel <[email protected]>
---
fs/fs-writeback.c | 39 +++++++++++++++---------
fs/hugetlbfs/inode.c | 2 -
fs/inode.c | 6 +--
fs/jfs/jfs_txnmgr.c | 9 +++++
fs/xfs/linux-2.6/xfs_iops.c | 4 +-
include/linux/fs.h | 70 ++++++++++++++++++++++++++++++++++++++------
include/linux/writeback.h | 7 ++++
mm/page-writeback.c | 2 -
8 files changed, 107 insertions(+), 32 deletions(-)
--- linux-2.6.21logfs/fs/fs-writeback.c~I_LOCK 2007-05-07 10:28:53.000000000 +0200
+++ linux-2.6.21logfs/fs/fs-writeback.c 2007-05-07 13:29:35.000000000 +0200
@@ -99,11 +99,11 @@ void __mark_inode_dirty(struct inode *in
inode->i_state |= flags;
/*
- * If the inode is locked, just update its dirty state.
+ * If the inode is being synced, just update its dirty state.
* The unlocker will place the inode on the appropriate
* superblock list, based upon its state.
*/
- if (inode->i_state & I_LOCK)
+ if (inode->i_state & I_SYNC)
goto out;
/*
@@ -139,6 +139,15 @@ static int write_inode(struct inode *ino
return 0;
}
+static void inode_sync_complete(struct inode *inode)
+{
+ /*
+ * Prevent speculative execution through spin_unlock(&inode_lock);
+ */
+ smp_mb();
+ wake_up_bit(&inode->i_state, __I_SYNC);
+}
+
/*
* Write a single inode's dirty pages and inode data out to disk.
* If `wait' is set, wait on the writeout.
@@ -158,11 +167,11 @@ __sync_single_inode(struct inode *inode,
int wait = wbc->sync_mode == WB_SYNC_ALL;
int ret;
- BUG_ON(inode->i_state & I_LOCK);
+ BUG_ON(inode->i_state & I_SYNC);
- /* Set I_LOCK, reset I_DIRTY */
+ /* Set I_SYNC, reset I_DIRTY */
dirty = inode->i_state & I_DIRTY;
- inode->i_state |= I_LOCK;
+ inode->i_state |= I_SYNC;
inode->i_state &= ~I_DIRTY;
spin_unlock(&inode_lock);
@@ -183,7 +192,7 @@ __sync_single_inode(struct inode *inode,
}
spin_lock(&inode_lock);
- inode->i_state &= ~I_LOCK;
+ inode->i_state &= ~I_SYNC;
if (!(inode->i_state & I_FREEING)) {
if (!(inode->i_state & I_DIRTY) &&
mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
@@ -231,7 +240,7 @@ __sync_single_inode(struct inode *inode,
list_move(&inode->i_list, &inode_unused);
}
}
- wake_up_inode(inode);
+ inode_sync_complete(inode);
return ret;
}
@@ -250,7 +259,7 @@ __writeback_single_inode(struct inode *i
else
WARN_ON(inode->i_state & I_WILL_FREE);
- if ((wbc->sync_mode != WB_SYNC_ALL) && (inode->i_state & I_LOCK)) {
+ if ((wbc->sync_mode != WB_SYNC_ALL) && (inode->i_state & I_SYNC)) {
struct address_space *mapping = inode->i_mapping;
int ret;
@@ -269,16 +278,16 @@ __writeback_single_inode(struct inode *i
/*
* It's a data-integrity sync. We must wait.
*/
- if (inode->i_state & I_LOCK) {
- DEFINE_WAIT_BIT(wq, &inode->i_state, __I_LOCK);
+ if (inode->i_state & I_SYNC) {
+ DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
- wqh = bit_waitqueue(&inode->i_state, __I_LOCK);
+ wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
do {
spin_unlock(&inode_lock);
__wait_on_bit(wqh, &wq, inode_wait,
TASK_UNINTERRUPTIBLE);
spin_lock(&inode_lock);
- } while (inode->i_state & I_LOCK);
+ } while (inode->i_state & I_SYNC);
}
return __sync_single_inode(inode, wbc);
}
@@ -311,7 +320,7 @@ __writeback_single_inode(struct inode *i
* The inodes to be written are parked on sb->s_io. They are moved back onto
* sb->s_dirty as they are selected for writing. This way, none can be missed
* on the writer throttling path, and we get decent balancing between many
- * throttled threads: we don't want them all piling up on __wait_on_inode.
+ * throttled threads: we don't want them all piling up on inode_sync_wait.
*/
static void
sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc)
@@ -583,7 +592,7 @@ int write_inode_now(struct inode *inode,
ret = __writeback_single_inode(inode, &wbc);
spin_unlock(&inode_lock);
if (sync)
- wait_on_inode(inode);
+ inode_sync_wait(inode);
return ret;
}
EXPORT_SYMBOL(write_inode_now);
@@ -658,7 +667,7 @@ int generic_osync_inode(struct inode *in
err = err2;
}
else
- wait_on_inode(inode);
+ inode_sync_wait(inode);
return err;
}
--- linux-2.6.21logfs/include/linux/fs.h~I_LOCK 2007-05-07 13:24:00.000000000 +0200
+++ linux-2.6.21logfs/include/linux/fs.h 2007-05-29 08:42:18.000000000 +0200
@@ -1174,16 +1174,68 @@ struct super_operations {
#endif
};
-/* Inode state bits. Protected by inode_lock. */
-#define I_DIRTY_SYNC 1 /* Not dirty enough for O_DATASYNC */
-#define I_DIRTY_DATASYNC 2 /* Data-related inode changes pending */
-#define I_DIRTY_PAGES 4 /* Data-related inode changes pending */
-#define __I_LOCK 3
+/*
+ * Inode state bits. Protected by inode_lock.
+ *
+ * Three bits determine the dirty state of the inode, I_DIRTY_SYNC,
+ * I_DIRTY_DATASYNC and I_DIRTY_PAGES.
+ *
+ * Four bits define the lifetime of an inode. Initially, inodes are I_NEW,
+ * until that flag is cleared. I_WILL_FREE, I_FREEING and I_CLEAR are set at
+ * various stages of removing an inode.
+ *
+ * Two bits are used for locking and completion notification, I_LOCK and I_SYNC.
+ *
+ * I_DIRTY_SYNC Inode itself is dirty.
+ * I_DIRTY_DATASYNC Data-related inode changes pending
+ * I_DIRTY_PAGES Inode has dirty pages. Inode itself may be clean.
+ * I_NEW get_new_inode() sets i_state to I_LOCK|I_NEW. Both
+ * are cleared by unlock_new_inode(), called from iget().
+ * I_WILL_FREE Must be set when calling write_inode_now() if i_count
+ * is zero. I_FREEING must be set when I_WILL_FREE is
+ * cleared.
+ * I_FREEING Set when inode is about to be freed but still has dirty
+ * pages or buffers attached or the inode itself is still
+ * dirty.
+ * I_CLEAR Set by clear_inode(). In this state the inode is clean
+ * and can be destroyed.
+ *
+ * Inodes that are I_WILL_FREE, I_FREEING or I_CLEAR are
+ * prohibited for many purposes. iget() must wait for
+ * the inode to be completely released, then create it
+ * anew. Other functions will just ignore such inodes,
+ * if appropriate. I_LOCK is used for waiting.
+ *
+ * I_LOCK Serves as both a mutex and completion notification.
+ * New inodes set I_LOCK. If two processes both create
+ * the same inode, one of them will release its inode and
+ * wait for I_LOCK to be released before returning.
+ * Inodes in I_WILL_FREE, I_FREEING or I_CLEAR state can
+ * also cause waiting on I_LOCK, without I_LOCK actually
+ * being set. find_inode() uses this to prevent returning
+ * nearly-dead inodes.
+ * I_SYNC Similar to I_LOCK, but limited in scope to writeback
+ * of inode dirty data. Having a seperate lock for this
+ * purpose reduces latency and prevents some filesystem-
+ * specific deadlocks.
+ *
+ * Q: Why does I_DIRTY_DATASYNC exist? It appears as if it could be replaced
+ * by (I_DIRTY_SYNC|I_DIRTY_PAGES).
+ * Q: What is the difference between I_WILL_FREE and I_FREEING?
+ * Q: igrab() only checks on (I_FREEING|I_WILL_FREE). Should it also check on
+ * I_CLEAR? If not, why?
+ */
+#define I_DIRTY_SYNC 1
+#define I_DIRTY_DATASYNC 2
+#define I_DIRTY_PAGES 4
+#define I_NEW 8
+#define I_WILL_FREE 16
+#define I_FREEING 32
+#define I_CLEAR 64
+#define __I_LOCK 7
#define I_LOCK (1 << __I_LOCK)
-#define I_FREEING 16
-#define I_CLEAR 32
-#define I_NEW 64
-#define I_WILL_FREE 128
+#define __I_SYNC 8
+#define I_SYNC (1 << __I_SYNC)
#define I_DIRTY (I_DIRTY_SYNC | I_DIRTY_DATASYNC | I_DIRTY_PAGES)
--- linux-2.6.21logfs/include/linux/writeback.h~I_LOCK 2007-05-07 13:24:01.000000000 +0200
+++ linux-2.6.21logfs/include/linux/writeback.h 2007-05-07 13:29:35.000000000 +0200
@@ -77,6 +77,13 @@ static inline void wait_on_inode(struct
wait_on_bit(&inode->i_state, __I_LOCK, inode_wait,
TASK_UNINTERRUPTIBLE);
}
+static inline void inode_sync_wait(struct inode *inode)
+{
+ might_sleep();
+ wait_on_bit(&inode->i_state, __I_SYNC, inode_wait,
+ TASK_UNINTERRUPTIBLE);
+}
+
/*
* mm/page-writeback.c
--- linux-2.6.21logfs/fs/inode.c~I_LOCK 2007-05-07 10:28:55.000000000 +0200
+++ linux-2.6.21logfs/fs/inode.c 2007-05-29 13:26:57.000000000 +0200
@@ -228,7 +228,7 @@ void __iget(struct inode * inode)
return;
}
atomic_inc(&inode->i_count);
- if (!(inode->i_state & (I_DIRTY|I_LOCK)))
+ if (!(inode->i_state & (I_DIRTY|I_SYNC)))
list_move(&inode->i_list, &inode_in_use);
inodes_stat.nr_unused--;
}
@@ -249,7 +249,7 @@ void clear_inode(struct inode *inode)
BUG_ON(inode->i_data.nrpages);
BUG_ON(!(inode->i_state & I_FREEING));
BUG_ON(inode->i_state & I_CLEAR);
- wait_on_inode(inode);
+ inode_sync_wait(inode);
DQUOT_DROP(inode);
if (inode->i_sb && inode->i_sb->s_op->clear_inode)
inode->i_sb->s_op->clear_inode(inode);
@@ -1038,7 +1038,7 @@ static void generic_forget_inode(struct
struct super_block *sb = inode->i_sb;
if (!hlist_unhashed(&inode->i_hash)) {
- if (!(inode->i_state & (I_DIRTY|I_LOCK)))
+ if (!(inode->i_state & (I_DIRTY|I_SYNC)))
list_move(&inode->i_list, &inode_unused);
inodes_stat.nr_unused++;
if (!sb || (sb->s_flags & MS_ACTIVE)) {
--- linux-2.6.21logfs/fs/jfs/jfs_txnmgr.c~I_LOCK 2007-05-07 10:28:55.000000000 +0200
+++ linux-2.6.21logfs/fs/jfs/jfs_txnmgr.c 2007-05-29 13:10:32.000000000 +0200
@@ -1286,7 +1286,14 @@ int txCommit(tid_t tid, /* transaction
* commit the transaction synchronously, so the last iput
* will be done by the calling thread (or later)
*/
- if (tblk->u.ip->i_state & I_LOCK)
+ /*
+ * I believe this code is no longer needed. Splitting I_LOCK
+ * into two bits, I_LOCK and I_SYNC should prevent this
+ * deadlock as well. But since I don't have a JFS testload
+ * to verify this, only a trivial s/I_LOCK/I_SYNC/ was done.
+ * Joern
+ */
+ if (tblk->u.ip->i_state & I_SYNC)
tblk->xflag &= ~COMMIT_LAZY;
}
--- linux-2.6.21logfs/fs/xfs/linux-2.6/xfs_iops.c~I_LOCK 2007-05-07 10:29:00.000000000 +0200
+++ linux-2.6.21logfs/fs/xfs/linux-2.6/xfs_iops.c 2007-05-29 13:15:14.000000000 +0200
@@ -133,7 +133,7 @@ xfs_ichgtime(
*/
SYNCHRONIZE();
ip->i_update_core = 1;
- if (!(inode->i_state & I_LOCK))
+ if (!(inode->i_state & I_SYNC))
mark_inode_dirty_sync(inode);
}
@@ -185,7 +185,7 @@ xfs_ichgtime_fast(
*/
SYNCHRONIZE();
ip->i_update_core = 1;
- if (!(inode->i_state & I_LOCK))
+ if (!(inode->i_state & I_SYNC))
mark_inode_dirty_sync(inode);
}
--- linux-2.6.21logfs/fs/hugetlbfs/inode.c~I_LOCK 2007-05-07 10:28:55.000000000 +0200
+++ linux-2.6.21logfs/fs/hugetlbfs/inode.c 2007-05-29 13:25:05.000000000 +0200
@@ -229,7 +229,7 @@ static void hugetlbfs_forget_inode(struc
struct super_block *sb = inode->i_sb;
if (!hlist_unhashed(&inode->i_hash)) {
- if (!(inode->i_state & (I_DIRTY|I_LOCK)))
+ if (!(inode->i_state & (I_DIRTY|I_SYNC)))
list_move(&inode->i_list, &inode_unused);
inodes_stat.nr_unused++;
if (!sb || (sb->s_flags & MS_ACTIVE)) {
--- linux-2.6.21logfs/mm/page-writeback.c~I_LOCK 2007-05-07 13:24:03.000000000 +0200
+++ linux-2.6.21logfs/mm/page-writeback.c 2007-05-29 13:28:10.000000000 +0200
@@ -36,7 +36,7 @@
/*
* The maximum number of pages to writeout in a single bdflush/kupdate
- * operation. We do this so we don't hold I_LOCK against an inode for
+ * operation. We do this so we don't hold I_SYNC against an inode for
* enormous amounts of time, which would block a userspace task which has
* been forced to throttle against that inode. Also, the code reevaluates
* the dirty each time it has written this many pages.
-
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