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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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