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Subject[PATCH 41/51] [GFS2] flocks from same process trip kernel BUG at fs/gfs2/glock.c:1118!
Date
From: Abhijith Das <adas@redhat.com>

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: Abhijith Das <adas@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 931368a..d631cad 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1106,24 +1106,31 @@ 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 (existing) {
- 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);
- 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",
- gl->gl_name.ln_type, gl->gl_state);
- BUG();
- }
-
- 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 "new: %s\n", gh->gh_ip);
- BUG();
+ 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);
+ 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);
+ 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",
+ gl->gl_name.ln_type, gl->gl_state);
+ BUG();
+ }
+
+ 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 "new: %s\n", gh->gh_ip);
+ BUG();
+ }
}

if (gh->gh_flags & LM_FLAG_PRIORITY)
diff --git a/fs/gfs2/glock.h b/fs/gfs2/glock.h
index f7a8e62..b16f604 100644
--- a/fs/gfs2/glock.h
+++ b/fs/gfs2/glock.h
@@ -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
diff --git a/fs/gfs2/ops_file.c b/fs/gfs2/ops_file.c
index 94d76ac..46a9e10 100644
--- a/fs/gfs2/ops_file.c
+++ b/fs/gfs2/ops_file.c
@@ -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);
}
-
- 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);
--
1.5.1.2
-
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