Messages in this thread Patch in this message | | | Date | Wed, 27 Sep 2006 18:43:03 +0530 | From | Srinivasa Ds <> | Subject | [RFC] Reverting "bd_mount_mutex" to "bd_mount_sem" |
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Hi all When I was executing "dmsetup resume <device-name>" command,I got the error shown below. Which basically tells that, "bd_mount_mutex" in thaw_bdev() is not locked by "dmsetup resume" command and hence it is not allowing it to unlock also. ========================================================= Badness in debug_mutex_unlock at kernel/mutex-debug.c:80
Call Trace: [C0000000634DB260] [C000000000010948] .show_stack+0x68/0x1b0 (unreliable) [C0000000634DB300] [C0000000003376C4] .program_check_exception+0x1cc/0x5b0 [C0000000634DB3D0] [C0000000000047EC] program_check_common+0xec/0x100 --- Exception: 700 at .debug_mutex_unlock+0x3c/0xc4 LR = .debug_mutex_unlock+0x30/0xc4 [C0000000634DB6C0] [C0000000634DB750] 0xc0000000634db750 (unreliable) [C0000000634DB740] [C000000000335950] .__mutex_unlock_slowpath+0xd8/0x144 [C0000000634DB7E0] [C0000000000E2370] .thaw_bdev+0x9c/0xb8 [C0000000634DB870] [D000000000480830] .unlock_fs+0x34/0x70 [dm_mod] [C0000000634DB900] [D000000000481720] .dm_resume+0x110/0x1ac [dm_mod] [C0000000634DB9A0] [D000000000485C54] .dev_suspend+0x1b0/0x204 [dm_mod] [C0000000634DBA40] [D000000000486728] .ctl_ioctl+0x29c/0x318 [dm_mod] [C0000000634DBC30] [C0000000000F8310] .do_ioctl+0xbc/0xf0 [C0000000634DBCD0] [C0000000000F879C] .vfs_ioctl+0x458/0x498 [C0000000634DBD80] [C0000000000F8874] .sys_ioctl+0x98/0xe0 [C0000000634DBE30] [C00000000000871C] syscall_exit+0x0/0x40 ======================================================================
On debugging I found out that,"dmsetup suspend <device name>" calls "freeze_bdev()",which locks "bd_mount_mutex" to make sure that no new mounts happen on bdev until thaw_bdev() is called. This "thaw_bdev()" is getting called when we resume the device through "dmsetup resume <device-name>". Hence we have 2 processes,one of which locks "bd_mount_mutex"(dmsetup suspend) and Another(dmsetup resume) unlocks it.
Since this is not allowed in mutex,I reverted back to bd_mount_sem(semaphore),It worked for me.
So need your comments for changing "bd_mount_mutex" to "bd_mount_sem". This is the patch,which I have used.
Thanks Srinivasa Ds LTC-IBM Bangalore
diff -Naurp linux-2.6.18-rc6-orig/fs/block_dev.c linux-2.6.18-rc6-mod/fs/block_dev.c --- linux-2.6.18-rc6-orig/fs/block_dev.c 2006-09-27 04:47:25.000000000 -0700 +++ linux-2.6.18-rc6-mod/fs/block_dev.c 2006-09-27 04:53:29.000000000 -0700 @@ -261,7 +261,7 @@ static void init_once(void * foo, kmem_c { memset(bdev, 0, sizeof(*bdev)); mutex_init(&bdev->bd_mutex); - mutex_init(&bdev->bd_mount_mutex); + sema_init(&bdev->bd_mount_sem, 1); INIT_LIST_HEAD(&bdev->bd_inodes); INIT_LIST_HEAD(&bdev->bd_list); #ifdef CONFIG_SYSFS diff -Naurp linux-2.6.18-rc6-orig/fs/buffer.c linux-2.6.18-rc6-mod/fs/buffer.c --- linux-2.6.18-rc6-orig/fs/buffer.c 2006-09-27 04:46:14.000000000 -0700 +++ linux-2.6.18-rc6-mod/fs/buffer.c 2006-09-27 04:49:55.000000000 -0700 @@ -213,7 +213,7 @@ struct super_block *freeze_bdev(struct b { struct super_block *sb; - mutex_lock(&bdev->bd_mount_mutex); + down(&bdev->bd_mount_sem); sb = get_super(bdev); if (sb && !(sb->s_flags & MS_RDONLY)) { sb->s_frozen = SB_FREEZE_WRITE; @@ -255,7 +255,7 @@ void thaw_bdev(struct block_device *bdev drop_super(sb); } - mutex_unlock(&bdev->bd_mount_mutex); + up(&bdev->bd_mount_sem); } EXPORT_SYMBOL(thaw_bdev); diff -Naurp linux-2.6.18-rc6-orig/fs/super.c linux-2.6.18-rc6-mod/fs/super.c --- linux-2.6.18-rc6-orig/fs/super.c 2006-09-27 04:46:51.000000000 -0700 +++ linux-2.6.18-rc6-mod/fs/super.c 2006-09-27 04:50:56.000000000 -0700 @@ -700,9 +700,9 @@ int get_sb_bdev(struct file_system_type * will protect the lockfs code from trying to start a snapshot * while we are mounting */ - mutex_lock(&bdev->bd_mount_mutex); + down(&bdev->bd_mount_sem); s = sget(fs_type, test_bdev_super, set_bdev_super, bdev); - mutex_unlock(&bdev->bd_mount_mutex); + up(&bdev->bd_mount_sem); if (IS_ERR(s)) goto error_s; diff -Naurp linux-2.6.18-rc6-orig/include/linux/fs.h linux-2.6.18-rc6-mod/include/linux/fs.h --- linux-2.6.18-rc6-orig/include/linux/fs.h 2006-09-27 04:45:31.000000000 -0700 +++ linux-2.6.18-rc6-mod/include/linux/fs.h 2006-09-27 04:52:30.000000000 -0700 @@ -414,7 +414,7 @@ struct block_device { struct inode * bd_inode; /* will die */ int bd_openers; struct mutex bd_mutex; /* open/close mutex */ - struct mutex bd_mount_mutex; /* mount mutex */ + struct semaphore bd_mount_sem; struct list_head bd_inodes; void * bd_holder; int bd_holders; | |