ext4: don't lock buffer in ext4_commit_super if holding spinlock

If there is an error reported in mballoc via ext4_grp_locked_error(),
the code is holding a spinlock, so ext4_commit_super() must not try to
lock the buffer head, or else it will trigger a BUG:

  BUG: sleeping function called from invalid context at ./include/linux/buffer_head.h:358
  in_atomic(): 1, irqs_disabled(): 0, pid: 993, name: mount
  CPU: 0 PID: 993 Comm: mount Not tainted 4.9.0-rc1-clouder1 #62
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.1-0-g4adadbd-20150316_085822-nilsson.home.kraxel.org 04/01/2014
   ffff880006423548 ffffffff81318c89 ffffffff819ecdd0 0000000000000166
   ffff880006423558 ffffffff810810b0 ffff880006423580 ffffffff81081153
   ffff880006e5a1a0 ffff88000690e400 0000000000000000 ffff8800064235c0
  Call Trace:
    [<ffffffff81318c89>] dump_stack+0x67/0x9e
    [<ffffffff810810b0>] ___might_sleep+0xf0/0x140
    [<ffffffff81081153>] __might_sleep+0x53/0xb0
    [<ffffffff8126c1dc>] ext4_commit_super+0x19c/0x290
    [<ffffffff8126e61a>] __ext4_grp_locked_error+0x14a/0x230
    [<ffffffff81081153>] ? __might_sleep+0x53/0xb0
    [<ffffffff812822be>] ext4_mb_generate_buddy+0x1de/0x320

Since ext4_grp_locked_error() calls ext4_commit_super with sync == 0
(and it is the only caller which does so), avoid locking and unlocking
the buffer in this case.

This can result in races with ext4_commit_super() if there are other
problems (which is what commit 4743f83990614 was trying to address),
but a Warning is better than BUG.

Fixes: 4743f83990614
Cc: stable@vger.kernel.org # 4.9
Reported-by: Nikolay Borisov <kernel@kyup.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index e4f61c39328a6b9d8fe16e4f047c51eda81e6066..ff6f3ab09c7ea2e171690f3d30ab9e86a41f8063 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4537,7 +4537,8 @@ static int ext4_commit_super(struct super_block *sb, int sync)
                                &EXT4_SB(sb)->s_freeinodes_counter));
        BUFFER_TRACE(sbh, "marking dirty");
        ext4_superblock_csum_set(sb);
-       lock_buffer(sbh);
+       if (sync)
+               lock_buffer(sbh);
        if (buffer_write_io_error(sbh)) {
                /*
                 * Oh, dear.  A previous attempt to write the
@@ -4553,8 +4554,8 @@ static int ext4_commit_super(struct super_block *sb, int sync)
                set_buffer_uptodate(sbh);
        }
        mark_buffer_dirty(sbh);
-       unlock_buffer(sbh);
        if (sync) {
+               unlock_buffer(sbh);
                error = __sync_dirty_buffer(sbh,
                        test_opt(sb, BARRIER) ? WRITE_FUA : WRITE_SYNC);
                if (error)