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    Subject[PATCH: 2.6.20-rc4-mm1] JFS: Avoid deadlock introduced by explicit I/O plugging
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    Jens,
    Can you please take a look at this patch, and if you think it's sane,
    add it to your explicit i/o plugging patchset? Would it make sense in
    any of these paths to use io_schedule() instead of schedule()?

    I hadn't looked at your patchset until I discovered that jfs was easy to
    hang in the -mm kernel. I think jfs may be able to add explicit
    plugging and unplugging in a couple of places, but I'd like to fix the
    hang right away and take my time with any later patches.

    Thanks,
    Shaggy

    JFS: Avoid deadlock introduced by explicit I/O plugging

    jfs is pretty easy to deadlock with Jens' explicit i/o plugging patchset.
    Just try building a kernel.

    The problem occurs when a synchronous transaction initiates some I/O, then
    waits in lmGroupCommit for the transaction to be committed to the journal.
    This requires action by the commit thread, which ends up waiting on a page
    to complete writeback. The commit thread did not initiate the I/O, so it
    cannot unplug the io queue, and deadlock occurs.

    The fix is for the first thread to call blk_replug_current_nested() before
    going to sleep. This patch also adds the call to a couple other places that
    look like they need it.

    Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>

    diff -Nurp linux-2.6.20-rc4-mm1/fs/jfs/jfs_lock.h linux/fs/jfs/jfs_lock.h
    --- linux-2.6.20-rc4-mm1/fs/jfs/jfs_lock.h 2006-11-29 15:57:37.000000000 -0600
    +++ linux/fs/jfs/jfs_lock.h 2007-01-17 15:30:19.000000000 -0600
    @@ -22,6 +22,7 @@
    #include <linux/spinlock.h>
    #include <linux/mutex.h>
    #include <linux/sched.h>
    +#include <linux/blkdev.h>

    /*
    * jfs_lock.h
    @@ -42,6 +43,7 @@ do { \
    if (cond) \
    break; \
    unlock_cmd; \
    + blk_replug_current_nested(); \
    schedule(); \
    lock_cmd; \
    } \
    diff -Nurp linux-2.6.20-rc4-mm1/fs/jfs/jfs_metapage.c linux/fs/jfs/jfs_metapage.c
    --- linux-2.6.20-rc4-mm1/fs/jfs/jfs_metapage.c 2007-01-12 09:50:45.000000000 -0600
    +++ linux/fs/jfs/jfs_metapage.c 2007-01-17 15:28:46.000000000 -0600
    @@ -23,6 +23,7 @@
    #include <linux/init.h>
    #include <linux/buffer_head.h>
    #include <linux/mempool.h>
    +#include <linux/blkdev.h>
    #include "jfs_incore.h"
    #include "jfs_superblock.h"
    #include "jfs_filsys.h"
    @@ -56,6 +57,7 @@ static inline void __lock_metapage(struc
    set_current_state(TASK_UNINTERRUPTIBLE);
    if (metapage_locked(mp)) {
    unlock_page(mp->page);
    + blk_replug_current_nested();
    schedule();
    lock_page(mp->page);
    }
    diff -Nurp linux-2.6.20-rc4-mm1/fs/jfs/jfs_txnmgr.c linux/fs/jfs/jfs_txnmgr.c
    --- linux-2.6.20-rc4-mm1/fs/jfs/jfs_txnmgr.c 2007-01-12 09:50:45.000000000 -0600
    +++ linux/fs/jfs/jfs_txnmgr.c 2007-01-17 15:29:04.000000000 -0600
    @@ -50,6 +50,7 @@
    #include <linux/module.h>
    #include <linux/moduleparam.h>
    #include <linux/kthread.h>
    +#include <linux/blkdev.h>
    #include "jfs_incore.h"
    #include "jfs_inode.h"
    #include "jfs_filsys.h"
    @@ -135,6 +136,7 @@ static inline void TXN_SLEEP_DROP_LOCK(w
    add_wait_queue(event, &wait);
    set_current_state(TASK_UNINTERRUPTIBLE);
    TXN_UNLOCK();
    + blk_replug_current_nested();
    schedule();
    current->state = TASK_RUNNING;
    remove_wait_queue(event, &wait);
    --
    David Kleikamp
    IBM Linux Technology Center

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