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Message-ID: <20180809130959.GH23873@fieldses.org>
Date: Thu, 9 Aug 2018 09:09:59 -0400
From: "J. Bruce Fields" <bfields@...ldses.org>
To: NeilBrown <neilb@...e.com>
Cc: Jeff Layton <jlayton@...nel.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
Martin Wilck <mwilck@...e.de>, linux-fsdevel@...r.kernel.org,
Frank Filz <ffilzlnx@...dspring.com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] fs/locks: change all *_conflict() functions to
return a new enum.
On Thu, Aug 09, 2018 at 12:04:41PM +1000, NeilBrown wrote:
> In a future patch we will need to differentiate between conflicts that
> are "transitive" and those that aren't.
> A "transitive" conflict is defined as one where any lock that
> conflicts with the first (newly requested) lock would conflict with
> the existing lock.
>
> So change posix_locks_conflict(), flock_locks_conflict() (both
> currently returning int) and leases_conflict() (currently returning
> bool) to return "enum conflict".
> Add locks_transitive_overlap() to make it possible to compute the
> correct conflict for posix locks.
>
> The FL_NO_CONFLICT value is zero, so current code which only tests the
> truth value of these functions will still work the same way.
>
> And convert some
> return (foo);
> to
> return foo;
>
> Signed-off-by: NeilBrown <neilb@...e.com>
> ---
> fs/locks.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++--------------
> 1 file changed, 49 insertions(+), 15 deletions(-)
>
> diff --git a/fs/locks.c b/fs/locks.c
> index b4812da2a374..d06658b2dc7a 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -139,6 +139,16 @@
> #define IS_OFDLCK(fl) (fl->fl_flags & FL_OFDLCK)
> #define IS_REMOTELCK(fl) (fl->fl_pid <= 0)
>
> +/* A transitive conflict is one where the first lock conflicts with
> + * the second lock, and any other lock that conflicts with the
> + * first lock, also conflicts with the second lock.
> + */
> +enum conflict {
> + FL_NO_CONFLICT = 0,
> + FL_CONFLICT,
> + FL_TRANSITIVE_CONFLICT,
> +};
> +
> static inline bool is_remote_lock(struct file *filp)
> {
> return likely(!(filp->f_path.dentry->d_sb->s_flags & SB_NOREMOTELOCK));
> @@ -612,6 +622,15 @@ static inline int locks_overlap(struct file_lock *fl1, struct file_lock *fl2)
> (fl2->fl_end >= fl1->fl_start));
> }
>
> +/* Check for transitive-overlap - true if any lock that overlaps
> + * the first lock must overlap the seconds
> + */
> +static inline bool locks_transitive_overlap(struct file_lock *fl1,
> + struct file_lock *fl2)
> +{
> + return (fl1->fl_start >= fl2->fl_start) &&
> + (fl1->fl_end <= fl2->fl_end);
> +}
> /*
> * Check whether two locks have the same owner.
> */
> @@ -793,47 +812,61 @@ locks_delete_lock_ctx(struct file_lock *fl, struct list_head *dispose)
> /* Determine if lock sys_fl blocks lock caller_fl. Common functionality
> * checks for shared/exclusive status of overlapping locks.
> */
> -static int locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
> +static enum conflict locks_conflict(struct file_lock *caller_fl,
> + struct file_lock *sys_fl)
> {
> if (sys_fl->fl_type == F_WRLCK)
> - return 1;
> + return FL_TRANSITIVE_CONFLICT;
> if (caller_fl->fl_type == F_WRLCK)
> - return 1;
> - return 0;
> + return FL_CONFLICT;
> + return FL_NO_CONFLICT;
> }
>
> /* Determine if lock sys_fl blocks lock caller_fl. POSIX specific
> * checking before calling the locks_conflict().
> */
> -static int posix_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
> +static enum conflict posix_locks_conflict(struct file_lock *caller_fl,
> + struct file_lock *sys_fl)
> {
> /* POSIX locks owned by the same process do not conflict with
> * each other.
> */
> if (posix_same_owner(caller_fl, sys_fl))
> - return (0);
> + return FL_NO_CONFLICT;
>
> /* Check whether they overlap */
> if (!locks_overlap(caller_fl, sys_fl))
> - return 0;
> + return FL_NO_CONFLICT;
>
> - return (locks_conflict(caller_fl, sys_fl));
> + switch (locks_conflict(caller_fl, sys_fl)) {
> + default:
> + case FL_NO_CONFLICT:
> + return FL_NO_CONFLICT;
> + case FL_CONFLICT:
> + return FL_CONFLICT;
If I'm understanding the logic here and in locks_conflict correctly,
you're telling me that in the case where sys_fl is a read lock, and
caller_fl is a write lock, then any lock which conflicts with sys_fl
must conflict with caller_fl? Or do I have that backwards? It doesn't
sound right, in any case.
--b.
> + case FL_TRANSITIVE_CONFLICT:
> + if (locks_transitive_overlap(caller_fl, sys_fl))
> + return FL_TRANSITIVE_CONFLICT;
> + else
> + return FL_CONFLICT;
> + }
> }
>
> /* Determine if lock sys_fl blocks lock caller_fl. FLOCK specific
> * checking before calling the locks_conflict().
> */
> -static int flock_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
> +static enum conflict flock_locks_conflict(struct file_lock *caller_fl,
> + struct file_lock *sys_fl)
> {
> /* FLOCK locks referring to the same filp do not conflict with
> * each other.
> */
> if (caller_fl->fl_file == sys_fl->fl_file)
> - return (0);
> + return FL_NO_CONFLICT;
> if ((caller_fl->fl_type & LOCK_MAND) || (sys_fl->fl_type & LOCK_MAND))
> - return 0;
> + return FL_NO_CONFLICT;
>
> - return (locks_conflict(caller_fl, sys_fl));
> + return locks_conflict(caller_fl, sys_fl);
> }
>
> void
> @@ -1435,12 +1468,13 @@ static void time_out_leases(struct inode *inode, struct list_head *dispose)
> }
> }
>
> -static bool leases_conflict(struct file_lock *lease, struct file_lock *breaker)
> +static enum conflict leases_conflict(struct file_lock *lease,
> + struct file_lock *breaker)
> {
> if ((breaker->fl_flags & FL_LAYOUT) != (lease->fl_flags & FL_LAYOUT))
> - return false;
> + return FL_NO_CONFLICT;
> if ((breaker->fl_flags & FL_DELEG) && (lease->fl_flags & FL_LEASE))
> - return false;
> + return FL_NO_CONFLICT;
> return locks_conflict(breaker, lease);
> }
>
>
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