[PATCH 3/3] locks: fix tracking of inprogress lease breaks
J. Bruce Fields
bfields at fieldses.org
Thu Jul 28 20:30:36 MDT 2011
From: J. Bruce Fields <bfields at redhat.com>
We currently use a bit in fl_flags to record whether a lease is being
broken, and set fl_type to the type (RDLCK or UNLCK) that it will
eventually have. This means that once the lease break starts, we forget
what the lease's type *used* to be. Breaking a read lease will then
result in blocking read opens, even though there's no conflict--because
the lease type is now F_UNLCK and we can no longer tell whether it was
previously a read or write lease.
So, instead keep fl_type as the original type (the type which we
enforce), and keep track of whether we're unlocking or merely
downgrading by replacing the single FL_INPROGRESS flag by
FL_UNLOCK_PENDING and FL_DOWNGRADE_PENDING flags.
To get this right we also need to track separate downgrade and break
times, to handle the case where a write-leased file gets conflicting
opens first for read, then later for write.
(I first considered just eliminating the downgrade behavior
completely--nfsv4 doesn't need it, and nobody as far as I can tell
actually uses it currently--but Jeremy Allison tells me that Windows
oplocks do behave this way, so Samba will probably use this some day.)
Signed-off-by: J. Bruce Fields <bfields at redhat.com>
---
fs/locks.c | 70 +++++++++++++++++++++++++++++++++++++--------------
include/linux/fs.h | 7 +++-
2 files changed, 56 insertions(+), 21 deletions(-)
diff --git a/fs/locks.c b/fs/locks.c
index c421541..d7089a8 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -135,7 +135,16 @@
static bool lease_breaking(struct file_lock *fl)
{
- return fl->fl_flags & FL_INPROGRESS;
+ return fl->fl_flags & (FL_UNLOCK_PENDING | FL_DOWNGRADE_PENDING);
+}
+
+static int target_leasetype(struct file_lock *fl)
+{
+ if (fl->fl_flags & FL_UNLOCK_PENDING)
+ return F_UNLCK;
+ if (fl->fl_flags & FL_DOWNGRADE_PENDING)
+ return F_RDLCK;
+ return fl->fl_type;
}
int leases_enable = 1;
@@ -1124,6 +1133,17 @@ int locks_mandatory_area(int read_write, struct inode *inode,
EXPORT_SYMBOL(locks_mandatory_area);
+int lease_clear_pending(struct file_lock *fl, int arg)
+{
+ switch (arg) {
+ case F_UNLCK:
+ fl->fl_flags &= ~FL_UNLOCK_PENDING;
+ /* fall through: */
+ case F_RDLCK:
+ fl->fl_flags &= ~FL_DOWNGRADE_PENDING;
+ }
+}
+
/* We already had a lease on this file; just change its type */
int lease_modify(struct file_lock **before, int arg)
{
@@ -1132,7 +1152,7 @@ int lease_modify(struct file_lock **before, int arg)
if (error)
return error;
- fl->fl_flags &= ~FL_INPROGRESS;
+ lease_clear_pending(fl, arg);
locks_wake_up_blocks(fl);
if (arg == F_UNLCK)
locks_delete_lock(before);
@@ -1141,6 +1161,14 @@ int lease_modify(struct file_lock **before, int arg)
EXPORT_SYMBOL(lease_modify);
+static bool past_time(unsigned long then)
+{
+ if (!then)
+ /* 0 is a special value meaning "this never expires": */
+ return false;
+ return time_after(jiffies, then);
+}
+
static void time_out_leases(struct inode *inode)
{
struct file_lock **before;
@@ -1148,12 +1176,10 @@ static void time_out_leases(struct inode *inode)
before = &inode->i_flock;
while ((fl = *before) && IS_LEASE(fl) && lease_breaking(fl)) {
- if ((fl->fl_break_time == 0)
- || time_before(jiffies, fl->fl_break_time)) {
- before = &fl->fl_next;
- continue;
- }
- lease_modify(before, fl->fl_type);
+ if (past_time(fl->fl_downgrade_time))
+ lease_modify(before, F_RDLCK);
+ if (past_time(fl->fl_break_time))
+ lease_modify(before, F_UNLCK);
if (fl == *before) /* lease_modify may have freed fl */
before = &fl->fl_next;
}
@@ -1194,13 +1220,13 @@ int __break_lease(struct inode *inode, unsigned int mode)
if (want_write) {
/* If we want write access, we have to revoke any lease. */
- future = F_UNLCK;
+ future = FL_UNLOCK_PENDING;
} else if (lease_breaking(flock)) {
/* If the lease is already being broken, we just leave it */
- future = flock->fl_type;
+ future = 0;
} else if (flock->fl_type & F_WRLCK) {
/* Downgrade the exclusive lease to a read-only lease. */
- future = F_RDLCK;
+ future = FL_DOWNGRADE_PENDING;
} else {
/* the existing lease was read-only, so we can read too. */
goto out;
@@ -1220,10 +1246,12 @@ int __break_lease(struct inode *inode, unsigned int mode)
}
for (fl = flock; fl && IS_LEASE(fl); fl = fl->fl_next) {
- if (fl->fl_type != future) {
- fl->fl_type = future;
- fl->fl_flags |= FL_INPROGRESS;
- fl->fl_break_time = break_time;
+ if (!(fl->fl_flags & future)) {
+ fl->fl_flags |= future;
+ if (future == FL_UNLOCK_PENDING)
+ fl->fl_break_time = break_time;
+ else /* FL_DOWNGRADE_PENDING */
+ fl->fl_downgrade_time = break_time;
/* lease must have lmops break callback */
fl->fl_lmops->lm_break(fl);
}
@@ -1250,10 +1278,14 @@ restart:
if (error >= 0) {
if (error == 0)
time_out_leases(inode);
- /* Wait for the next lease that has not been broken yet */
+ /*
+ * Wait for the next conflicting lease that has not been
+ * broken yet
+ */
for (flock = inode->i_flock; flock && IS_LEASE(flock);
flock = flock->fl_next) {
- if (lease_breaking(flock))
+ if ((want_write && flock->fl_type == F_RDLCK)
+ || flock->fl_type == F_WRLCK)
goto restart;
}
error = 0;
@@ -1321,7 +1353,7 @@ int fcntl_getlease(struct file *filp)
for (fl = filp->f_path.dentry->d_inode->i_flock; fl && IS_LEASE(fl);
fl = fl->fl_next) {
if (fl->fl_file == filp) {
- type = fl->fl_type;
+ type = target_leasetype(fl);
break;
}
}
@@ -1386,7 +1418,7 @@ int generic_setlease(struct file *filp, long arg, struct file_lock **flp)
before = &fl->fl_next) {
if (fl->fl_file == filp)
my_before = before;
- else if ((fl->fl_type == F_UNLCK) && lease_breaking(fl))
+ else if (fl->fl_flags & FL_UNLOCK_PENDING)
/*
* Someone is in the process of opening this
* file for writing so we may not take an
diff --git a/include/linux/fs.h b/include/linux/fs.h
index f0b692c..225676c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1050,7 +1050,8 @@ static inline int file_check_writeable(struct file *filp)
#define FL_LEASE 32 /* lease held on this file */
#define FL_CLOSE 64 /* unlock on close */
#define FL_SLEEP 128 /* A blocking lock */
-#define FL_INPROGRESS 256 /* Lease is being broken */
+#define FL_UNLOCK_PENDING 256 /* Lease is being broken */
+#define FL_DOWNGRADE_PENDING 512 /* Lease is being downgraded */
/*
* Special return value from posix_lock_file() and vfs_lock_file() for
@@ -1107,7 +1108,9 @@ struct file_lock {
loff_t fl_end;
struct fasync_struct * fl_fasync; /* for lease break notifications */
- unsigned long fl_break_time; /* for nonblocking lease breaks */
+ /* for lease breaks: */
+ unsigned long fl_break_time;
+ unsigned long fl_downgrade_time;
const struct file_lock_operations *fl_ops; /* Callbacks for filesystems */
const struct lock_manager_operations *fl_lmops; /* Callbacks for lockmanagers */
--
1.7.4.1
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