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locks: fix tracking of inprogress lease breaks 

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.)

Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
This commit is contained in:
J. Bruce Fields 2011-07-26 18:25:49 -04:00
parent 710b721696
commit 778fc546f7
2 changed files with 60 additions and 34 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

87
fs/locks.c
View File

@ -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);
static void 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;
}
@ -1171,7 +1197,7 @@ static void time_out_leases(struct inode *inode)
*/
int __break_lease(struct inode *inode, unsigned int mode)
{
int error = 0, future;
int error = 0;
struct file_lock *new_fl, *flock;
struct file_lock *fl;
unsigned long break_time;
@ -1188,24 +1214,13 @@ int __break_lease(struct inode *inode, unsigned int mode)
if ((flock == NULL) || !IS_LEASE(flock))
goto out;
if (!locks_conflict(flock, new_fl))
goto out;
for (fl = flock; fl && IS_LEASE(fl); fl = fl->fl_next)
if (fl->fl_owner == current->files)
i_have_this_lease = 1;
if (want_write) {
/* If we want write access, we have to revoke any lease. */
future = F_UNLCK;
} else if (lease_breaking(flock)) {
/* If the lease is already being broken, we just leave it */
future = flock->fl_type;
} else if (flock->fl_type & F_WRLCK) {
/* Downgrade the exclusive lease to a read-only lease. */
future = F_RDLCK;
} else {
/* the existing lease was read-only, so we can read too. */
goto out;
}
if (IS_ERR(new_fl) && !i_have_this_lease
&& ((mode & O_NONBLOCK) == 0)) {
error = PTR_ERR(new_fl);
@ -1220,13 +1235,18 @@ 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;
if (want_write) {
if (fl->fl_flags & FL_UNLOCK_PENDING)
continue;
fl->fl_flags |= FL_UNLOCK_PENDING;
fl->fl_break_time = break_time;
/* lease must have lmops break callback */
fl->fl_lmops->lm_break(fl);
} else {
if (lease_breaking(flock))
continue;
fl->fl_flags |= FL_DOWNGRADE_PENDING;
fl->fl_downgrade_time = break_time;
}
fl->fl_lmops->lm_break(fl);
}
if (i_have_this_lease || (mode & O_NONBLOCK)) {
@ -1250,10 +1270,13 @@ 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 (locks_conflict(new_fl, flock))
goto restart;
}
error = 0;
@ -1321,7 +1344,7 @@ 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 +1409,7 @@ 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

7
include/linux/fs.h
View File

@ -1065,7 +1065,8 @@ 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_DOWNGRADE_PENDING 256 /* Lease is being downgraded */
#define FL_UNLOCK_PENDING 512 /* Lease is being broken */
/*
* Special return value from posix_lock_file() and vfs_lock_file() for
@ -1122,7 +1123,9 @@ 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 */