lkml.org 
[lkml]   [2016]   [Aug]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 4.6 46/56] fs/dcache.c: avoid soft-lockup in dput()
    Date
    4.6-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Wei Fang <fangwei1@huawei.com>

    commit 47be61845c775643f1aa4d2a54343549f943c94c upstream.

    We triggered soft-lockup under stress test which
    open/access/write/close one file concurrently on more than
    five different CPUs:

    WARN: soft lockup - CPU#0 stuck for 11s! [who:30631]
    ...
    [<ffffffc0003986f8>] dput+0x100/0x298
    [<ffffffc00038c2dc>] terminate_walk+0x4c/0x60
    [<ffffffc00038f56c>] path_lookupat+0x5cc/0x7a8
    [<ffffffc00038f780>] filename_lookup+0x38/0xf0
    [<ffffffc000391180>] user_path_at_empty+0x78/0xd0
    [<ffffffc0003911f4>] user_path_at+0x1c/0x28
    [<ffffffc00037d4fc>] SyS_faccessat+0xb4/0x230

    ->d_lock trylock may failed many times because of concurrently
    operations, and dput() may execute a long time.

    Fix this by replacing cpu_relax() with cond_resched().
    dput() used to be sleepable, so make it sleepable again
    should be safe.

    Signed-off-by: Wei Fang <fangwei1@huawei.com>
    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/dcache.c | 7 +++++--
    1 file changed, 5 insertions(+), 2 deletions(-)

    --- a/fs/dcache.c
    +++ b/fs/dcache.c
    @@ -578,7 +578,6 @@ static struct dentry *dentry_kill(struct

    failed:
    spin_unlock(&dentry->d_lock);
    - cpu_relax();
    return dentry; /* try again with same dentry */
    }

    @@ -752,6 +751,8 @@ void dput(struct dentry *dentry)
    return;

    repeat:
    + might_sleep();
    +
    rcu_read_lock();
    if (likely(fast_dput(dentry))) {
    rcu_read_unlock();
    @@ -783,8 +784,10 @@ repeat:

    kill_it:
    dentry = dentry_kill(dentry);
    - if (dentry)
    + if (dentry) {
    + cond_resched();
    goto repeat;
    + }
    }
    EXPORT_SYMBOL(dput);


    \
     
     \ /
      Last update: 2016-09-17 09:56    [W:3.149 / U:0.888 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site