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Commit b4c20166 authored by Abhijith Das's avatar Abhijith Das Committed by Steven Whitehouse
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[GFS2] flocks from same process trip kernel BUG at fs/gfs2/glock.c:1118! 



This patch adds a new flag to the gfs2_holder structure GL_FLOCK.
It is set on holders of glocks representing flocks. This flag is
checked in add_to_queue() and a process is permitted to queue more
than one holder onto a glock if it is set. This solves the issue
of a process not being able to do multiple flocks on the same file.
Through a single descriptor, a process can now promote and demote
flocks. Through multiple descriptors a process can now queue
multiple flocks on the same file. There's still the problem of
a process deadlocking itself (because gfs2 blocking locks are not
interruptible) by queueing incompatible deadlock.

Signed-off-by: default avatarAbhijith Das <adas@redhat.com>
Signed-off-by: default avatarSteven Whitehouse <swhiteho@redhat.com>
parent 1ad38c43

fs/gfs2/glock.c

+25 −18
Original line number Diff line number Diff line
@@ -1106,12 +1106,16 @@ static void add_to_queue(struct gfs2_holder *gh) 
	if (test_and_set_bit(HIF_WAIT, &gh->gh_iflags))

		BUG();



	existing = find_holder_by_owner(&gl->gl_holders, gh->gh_owner_pid);

	if (!(gh->gh_flags & GL_FLOCK)) {

		existing = find_holder_by_owner(&gl->gl_holders, 

						gh->gh_owner_pid);

		if (existing) {

		print_symbol(KERN_WARNING "original: %s\n", existing->gh_ip);

			print_symbol(KERN_WARNING "original: %s\n", 

				     existing->gh_ip);

			printk(KERN_INFO "pid : %d\n", existing->gh_owner_pid);

			printk(KERN_INFO "lock type : %d lock state : %d\n",

				existing->gh_gl->gl_name.ln_type, existing->gh_gl->gl_state);

			       existing->gh_gl->gl_name.ln_type, 

			       existing->gh_gl->gl_state);

			print_symbol(KERN_WARNING "new: %s\n", gh->gh_ip);

			printk(KERN_INFO "pid : %d\n", gh->gh_owner_pid);

			printk(KERN_INFO "lock type : %d lock state : %d\n",
@@ -1119,12 +1123,15 @@ static void add_to_queue(struct gfs2_holder *gh) 
			BUG();

		}

		

	existing = find_holder_by_owner(&gl->gl_waiters3, gh->gh_owner_pid);

		existing = find_holder_by_owner(&gl->gl_waiters3, 

						gh->gh_owner_pid);

		if (existing) {

		print_symbol(KERN_WARNING "original: %s\n", existing->gh_ip);

			print_symbol(KERN_WARNING "original: %s\n", 

				     existing->gh_ip);

			print_symbol(KERN_WARNING "new: %s\n", gh->gh_ip);

			BUG();

		}

	}



	if (gh->gh_flags & LM_FLAG_PRIORITY)

		list_add(&gh->gh_list, &gl->gl_waiters3);

fs/gfs2/glock.h

+1 −0
Original line number Diff line number Diff line
@@ -26,6 +26,7 @@ 
#define GL_SKIP			0x00000100

#define GL_ATIME		0x00000200

#define GL_NOCACHE		0x00000400

#define GL_FLOCK		0x00000800

#define GL_NOCANCEL		0x00001000



#define GLR_TRYFAILED		13

fs/gfs2/ops_file.c

+6 −7
Original line number Diff line number Diff line
@@ -571,7 +571,8 @@ static int do_flock(struct file *file, int cmd, struct file_lock *fl) 
	int error = 0;



	state = (fl->fl_type == F_WRLCK) ? LM_ST_EXCLUSIVE : LM_ST_SHARED;

	flags = (IS_SETLKW(cmd) ? 0 : LM_FLAG_TRY) | GL_EXACT | GL_NOCACHE;

	flags = (IS_SETLKW(cmd) ? 0 : LM_FLAG_TRY) | GL_EXACT | GL_NOCACHE 

		| GL_FLOCK;



	mutex_lock(&fp->f_fl_mutex);
@@ -579,21 +580,19 @@ static int do_flock(struct file *file, int cmd, struct file_lock *fl) 
	if (gl) {

		if (fl_gh->gh_state == state)

			goto out;

		gfs2_glock_hold(gl);

		flock_lock_file_wait(file,

				     &(struct file_lock){.fl_type = F_UNLCK});

		gfs2_glock_dq_uninit(fl_gh);

		gfs2_glock_dq_wait(fl_gh);

		gfs2_holder_reinit(state, flags, fl_gh);

	} else {

		error = gfs2_glock_get(GFS2_SB(&ip->i_inode),

				      ip->i_no_addr, &gfs2_flock_glops,

				      CREATE, &gl);

		if (error)

			goto out;

	}



		gfs2_holder_init(gl, state, flags, fl_gh);

		gfs2_glock_put(gl);



	}

	error = gfs2_glock_nq(fl_gh);

	if (error) {

		gfs2_holder_uninit(fl_gh);