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    Subject[PATCH AUTOSEL 4.19 25/25] ocfs2: ocfs2_downconvert_lock failure results in deadlock
    Date
    From: Gang He <ghe@suse.com>

    [ Upstream commit 9673e0050c39b0534d0e2ca431223f52089f4959 ]

    Usually, ocfs2_downconvert_lock() function always downconverts dlm lock to
    the expected level for satisfy dlm bast requests from the other nodes.

    But there is a rare situation. When dlm lock conversion is being
    canceled, ocfs2_downconvert_lock() function will return -EBUSY. You need
    to be aware that ocfs2_cancel_convert() function is asynchronous in fsdlm
    implementation.

    If we does not requeue this lockres entry, ocfs2 downconvert thread no
    longer handles this dlm lock bast request. Then, the other nodes will not
    get the dlm lock again, the current node's process will be blocked when
    acquire this dlm lock again.

    Link: https://lkml.kernel.org/r/20210830044621.12544-1-ghe@suse.com
    Signed-off-by: Gang He <ghe@suse.com>
    Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
    Cc: Mark Fasheh <mark@fasheh.com>
    Cc: Joel Becker <jlbec@evilplan.org>
    Cc: Junxiao Bi <junxiao.bi@oracle.com>
    Cc: Changwei Ge <gechangwei@live.cn>
    Cc: Gang He <ghe@suse.com>
    Cc: Jun Piao <piaojun@huawei.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/ocfs2/dlmglue.c | 12 ++++++++++++
    1 file changed, 12 insertions(+)

    diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
    index 8149fb6f1f0d..496d16376764 100644
    --- a/fs/ocfs2/dlmglue.c
    +++ b/fs/ocfs2/dlmglue.c
    @@ -32,6 +32,7 @@
    #include <linux/debugfs.h>
    #include <linux/seq_file.h>
    #include <linux/time.h>
    +#include <linux/delay.h>
    #include <linux/quotaops.h>
    #include <linux/sched/signal.h>

    @@ -3880,6 +3881,17 @@ static int ocfs2_unblock_lock(struct ocfs2_super *osb,
    spin_unlock_irqrestore(&lockres->l_lock, flags);
    ret = ocfs2_downconvert_lock(osb, lockres, new_level, set_lvb,
    gen);
    + /* The dlm lock convert is being cancelled in background,
    + * ocfs2_cancel_convert() is asynchronous in fs/dlm,
    + * requeue it, try again later.
    + */
    + if (ret == -EBUSY) {
    + ctl->requeue = 1;
    + mlog(ML_BASTS, "lockres %s, ReQ: Downconvert busy\n",
    + lockres->l_name);
    + ret = 0;
    + msleep(20);
    + }

    leave:
    if (ret)
    --
    2.30.2
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