Re: 2.4.2-ac3: loop threads in D state

[Jens Axboe]

On Sun, Feb 25 2001, Alexander Viro wrote:
> > >   if (atomic_dec_and_test(...))
> > >           up(...);
> > > not just
> > >   atomic_dec(...);
> > >   up(...);
> > > 
> > > Otherwise you can end up with too early exit of loop_thread. Normally
> > > it would not matter, but in pathological cases...
> > 
> > How so? We dec it and up the semaphore, loop_thread runs until it's
> > done and ups lo_sem.
> 
> You are risking an extra up() here. Think what happens if you already had a
> pending request.

Ah ok, I see what you mean. Updated patch attached.

-- 
Jens Axboe


diff -ur --exclude-from /home/axboe/cdrom/exclude 
/opt/kernel/linux-2.4.2-ac4/drivers/block/loop.c linux/drivers/block/loop.c
--- /opt/kernel/linux-2.4.2-ac4/drivers/block/loop.c    Mon Feb 26 01:19:38 2001
+++ linux/drivers/block/loop.c  Mon Feb 26 01:38:36 2001
@@ -79,7 +79,6 @@
 static int *loop_sizes;
 static int *loop_blksizes;
 static devfs_handle_t devfs_handle;      /*  For the directory */
-static kmem_cache_t *loop_bhp;
 
 /*
  * Transfer functions
@@ -289,7 +288,7 @@
        if (bh) {
                kunmap(bh->b_page);
                __free_page(bh->b_page);
-               kmem_cache_free(loop_bhp, bh);
+               kmem_cache_free(bh_cachep, bh);
        }
 }
 
@@ -358,7 +357,7 @@
        struct buffer_head *bh;
 
        do {
-               bh = kmem_cache_alloc(loop_bhp, SLAB_BUFFER);
+               bh = kmem_cache_alloc(bh_cachep, SLAB_BUFFER);
                if (bh)
                        break;
 
@@ -508,7 +507,7 @@
        sprintf(current->comm, "loop%d", lo->lo_number);
 
        spin_lock_irq(&current->sigmask_lock);
-       siginitsetinv(&current->blocked, sigmask(SIGKILL));
+       sigfillset(&current->blocked);
        flush_signals(current);
        spin_unlock_irq(&current->sigmask_lock);
 
@@ -526,7 +525,7 @@
        up(&lo->lo_sem);
 
        for (;;) {
-               down(&lo->lo_bh_mutex);
+               down_interruptible(&lo->lo_bh_mutex);
                if (!atomic_read(&lo->lo_pending))
                        break;
 
@@ -671,9 +670,12 @@
        if (lo->lo_refcnt > 1)  /* we needed one fd for the ioctl */
                return -EBUSY;
 
+       spin_lock_irq(&lo->lo_lock);
        lo->lo_state = Lo_rundown;
-       atomic_dec(&lo->lo_pending);
-       up(&lo->lo_bh_mutex);
+       if (atomic_dec_and_test(&lo->lo_pending))
+               up(&lo->lo_bh_mutex);
+       spin_unlock_irq(&lo->lo_lock);
+
        down(&lo->lo_sem);
 
        lo->lo_backing_file = NULL;
@@ -927,13 +929,6 @@
                return -EIO;
        }
 
-       loop_bhp = kmem_cache_create("loop_buffers", sizeof(struct buffer_head),
-                                    0, SLAB_HWCACHE_ALIGN, NULL, NULL);
-       if (!loop_bhp) {
-               printk(KERN_WARNING "loop: unable to create slab cache\n");
-               return -ENOMEM;
-       }
-                               
        devfs_handle = devfs_mk_dir(NULL, "loop", NULL);
        devfs_register_series(devfs_handle, "%u", max_loop, DEVFS_FL_DEFAULT,
                              MAJOR_NR, 0,
@@ -942,7 +937,7 @@
 
        loop_dev = kmalloc(max_loop * sizeof(struct loop_device), GFP_KERNEL);
        if (!loop_dev)
-               goto out_dev;
+               return -ENOMEM;
 
        loop_sizes = kmalloc(max_loop * sizeof(int), GFP_KERNEL);
        if (!loop_sizes)
@@ -974,8 +969,6 @@
        printk(KERN_INFO "loop: loaded (max %d devices)\n", max_loop);
        return 0;
 
-out_dev:
-       kmem_cache_destroy(loop_bhp);
 out_sizes:
        kfree(loop_dev);
 out_blksizes:
@@ -990,7 +983,6 @@
        if (devfs_unregister_blkdev(MAJOR_NR, "loop"))
                printk(KERN_WARNING "loop: cannot unregister blkdev\n");
 
-       kmem_cache_destroy(loop_bhp);
        kfree(loop_dev);
        kfree(loop_sizes);
        kfree(loop_blksizes);
diff -ur --exclude-from /home/axboe/cdrom/exclude 
/opt/kernel/linux-2.4.2-ac4/fs/Makefile linux/fs/Makefile
--- /opt/kernel/linux-2.4.2-ac4/fs/Makefile     Mon Feb 26 01:19:40 2001
+++ linux/fs/Makefile   Mon Feb 26 01:14:44 2001
@@ -7,7 +7,7 @@
 
 O_TARGET := fs.o
 
-export-objs := filesystems.o open.o
+export-objs := filesystems.o open.o dcache.o
 mod-subdirs := nls
 
 obj-y :=       open.o read_write.o devices.o file_table.o buffer.o \
diff -ur --exclude-from /home/axboe/cdrom/exclude 
/opt/kernel/linux-2.4.2-ac4/fs/dcache.c linux/fs/dcache.c
--- /opt/kernel/linux-2.4.2-ac4/fs/dcache.c     Sat Feb 17 01:06:17 2001
+++ linux/fs/dcache.c   Mon Feb 26 01:14:54 2001
@@ -22,6 +22,7 @@
 #include <linux/init.h>
 #include <linux/smp_lock.h>
 #include <linux/cache.h>
+#include <linux/module.h>
 
 #include <asm/uaccess.h>
 
@@ -1250,6 +1251,7 @@
 
 /* SLAB cache for buffer_head structures */
 kmem_cache_t *bh_cachep;
+EXPORT_SYMBOL(bh_cachep);
 
 void __init vfs_caches_init(unsigned long mempages)
 {