[tip:sched/core,16/27] fs/jbd/commit.c:105:12: sparse: context imbalance in 'inverted_lock' - wrong count at exit

From: Peter Zijlstra <peterz@infradead.org>

On Thu, Sep 26, 2013 at 02:31:09AM +0800, kbuild test robot wrote:
> tree:   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched/core
> head:   1a338ac32ca630f67df25b4a16436cccc314e997
> commit: 0c44c2d0f459cd7e275242b72f500137c4fa834d [16/27] x86: Use asm goto to implement better modify_and_test() functions
> reproduce: make C=1 CF=-D__CHECK_ENDIAN__
> 
> 
> sparse warnings: (new ones prefixed by >>)
> 
> >> fs/jbd/commit.c:105:12: sparse: context imbalance in 'inverted_lock' - wrong count at exit
>    fs/jbd/commit.c:205:9: sparse: context imbalance in 'journal_submit_data_buffers' - different lock contexts for basic block
>    fs/jbd/commit.c:456:9: sparse: context imbalance in 'journal_commit_transaction' - different lock contexts for basic block
> --
>    include/linux/bit_spinlock.h:62:25: sparse: context imbalance in '__try_to_free_cp_buf' - unexpected unlock
>    fs/jbd/checkpoint.c:155:36: sparse: context imbalance in '__log_wait_for_space' - unexpected unlock
>    include/linux/bit_spinlock.h:62:25: sparse: context imbalance in '__wait_cp_io' - unexpected unlock
>    fs/jbd/checkpoint.c:294:23: sparse: context imbalance in '__process_buffer' - unexpected unlock
>    fs/jbd/checkpoint.c:390:9: sparse: context imbalance in 'log_do_checkpoint' - different lock contexts for basic block
> >> fs/jbd/checkpoint.c:557:12: sparse: context imbalance in 'journal_clean_one_cp_list' - wrong count at exit
> --
> >> drivers/infiniband/hw/qib/qib_verbs.h:1061:36: sparse: crazy programmer
> 
> vim +/inverted_lock +105 fs/jbd/commit.c
> 
>     89			WARN_ON_ONCE(buffer_dirty(bh));
>     90			clear_buffer_freed(bh);
>     91			clear_buffer_mapped(bh);
>     92			clear_buffer_new(bh);
>     93			clear_buffer_req(bh);
>     94			bh->b_bdev = NULL;
>     95			release_buffer_page(bh);
>     96		} else
>     97			put_bh(bh);
>     98	}
>     99	
>    100	/*
>    101	 * Try to acquire jbd_lock_bh_state() against the buffer, when j_list_lock is
>    102	 * held.  For ranking reasons we must trylock.  If we lose, schedule away and
>    103	 * return 0.  j_list_lock is dropped in this case.
>    104	 */
>  > 105	static int inverted_lock(journal_t *journal, struct buffer_head *bh)
>    106	{
>    107		if (!jbd_trylock_bh_state(bh)) {
>    108			spin_unlock(&journal->j_list_lock);
>    109			schedule();
>    110			return 0;
>    111		}
>    112		return 1;
>    113	}

I've really no idea how that patch can cause sparse warnings. Patch
included below for the sparse people. Does sparse presume to understand
inline asm?

---
Subject: x86: Use asm goto to implement better modify_and_test() functions
From: Peter Zijlstra <peterz@infradead.org>
Date: Wed Sep 11 15:19:24 CEST 2013

Linus suggested using asm goto to get rid of the typical SETcc + TEST
instruction pair -- which also clobbers an extra register -- for our
typical modify_and_test() functions.

Because asm goto doesn't allow output fields it has to include an
unconditinal memory clobber when it changes a memory variable to force
a reload.

Luckily all atomic ops already imply a compiler barrier to go along
with their memory barrier semantics.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
---
 arch/x86/include/asm/atomic.h      |   29 ++++----------------------
 arch/x86/include/asm/atomic64_64.h |   28 +++----------------------
 arch/x86/include/asm/bitops.h      |   24 +++------------------
 arch/x86/include/asm/local.h       |   28 +++----------------------
 arch/x86/include/asm/rmwcc.h       |   41 +++++++++++++++++++++++++++++++++++++
 5 files changed, 58 insertions(+), 92 deletions(-)

--
To unsubscribe from this list: send the line "unsubscribe linux-sparse" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[tip:sched/core,16/27] fs/jbd/commit.c:105:12: sparse: context imbalance in 'inverted_lock' - wrong count at exit

Commit Message

Comments

Patch