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Date: Wed, 16 Mar 2005 11:47:25 -0500 (EST)
From: Steven Rostedt <rostedt@goodmis.org>
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To: Andrew Morton <akpm@osdl.org>
cc: mingo@elte.hu, rlrevell@joe-job.com, linux-kernel@vger.kernel.org
Subject: Re: [patch 0/3] j_state_lock, j_list_lock, remove-bitlocks
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On Wed, 16 Mar 2005, Steven Rostedt wrote:
>
> Ingo, I still get the following bug because of the added BUFFER_FNS and
> DESKTOP_PREEMPT.  I haven't tried this with RT yet. I'll see if this shows
> a deadlock there.
>
>

Hi Ingo,

I just ran this with PREEMPT_RT and it works fine.  Now is this the best
solution, or adding a lock to the buffer head?  This works but I don't
have anything more than a 2X CPU to test this on.  If either you or Andrew
can try this on the 8x or 16x that would be great..

Also, I only get the BUG with PREEMPT_DESKTOP.  I really don't understand
why this happens. I sent you a test patch earlier with just adding
BUFFER_FNS(JournalHead,journalhead) in jbd.h, and under PREEMPT_DESKTOP
that causes this bug as well. No other changes, just adding the BUFFER_FNS
call causes this. I can't find any other reference to buffer_journal
(besides reiser_fs).  What do you think, and are you getting the same bug?

-- Steve


> BUG: Unable to handle kernel NULL pointer dereference at virtual address
> 00000000
>  printing eip:
> c0214888
> *pde = 00000000
> Oops: 0000 [#1]
> Modules linked in: ipv6 af_packet tsdev mousedev evdev floppy psmouse
> pcspkr snd_intel8x0 snd_ac97_codec snd_pcm_oss snd_mixer_oss snd_pcm
> snd_timer snd soundcore snd_page_alloc shpchp pci_hotplug ehci_hcd
> intel_agp agpgart uhci_hcd usbcore e100 mii ide_cd cdrom unix
> CPU:    0
> EIP:    0060:[<c0214888>]    Not tainted VLI
> EFLAGS: 00010286   (2.6.11-RT-V0.7.40-00)
> EIP is at vt_ioctl+0x18/0x1ab0
> eax: 00000000   ebx: 00005603   ecx: 00005603   edx: cec18c80
> esi: c0214870   edi: cb49e000   ebp: cb479f18   esp: cb479e48
> ds: 007b   es: 007b   ss: 0068   preempt: 00000000
> Process XFree86 (pid: 4744, threadinfo=cb478000 task=cb403530)
> Stack: cb403680 cb478000 cb403530 c034594c cb403530 00000246 cb479e7c
> c0117217
>        c0345954 00000006 00000001 00000000 00000000 cb479ebc cefa1c04
> c13e1000
>        ced6b9b8 00000000 00000000 cb479ed4 c01707f1 ced6b9b8 00000007
> 00000000
> Call Trace:
>  [<c0103cdf>] show_stack+0x7f/0xa0 (28)
>  [<c0103e95>] show_registers+0x165/0x1d0 (56)
>  [<c0104088>] die+0xc8/0x150 (64)
>  [<c0115376>] do_page_fault+0x356/0x6c4 (216)
>  [<c0103973>] error_code+0x2b/0x30 (268)
>  [<c020fd6b>] tty_ioctl+0x34b/0x490 (52)
>  [<c016837f>] do_ioctl+0x4f/0x70 (32)
>  [<c0168582>] vfs_ioctl+0x62/0x1d0 (40)
>  [<c0168751>] sys_ioctl+0x61/0x90 (40)
>  [<c0102ec3>] syscall_call+0x7/0xb (-8124)
> Code: ff ff 8d 05 88 5d 34 c0 e8 f6 60 0a 00 e9 3a ff ff ff 90 55 89 e5 57
> 56 53 81 ec c4 00 00 00 8b 7d 08 8b 5d 10 8b 87 7c 09 00 00 <8b> 30 89 34
> 24 8b 04 b5 e0 b7 3c c0 89 45 8c e8 a4 6a 00 00 85
>
>
>
>
> Here's the patch (on Ingo's -40 kernel).
>
> diff -ur linux-2.6.11-final-V0.7.40-00.orig/fs/jbd/journal.c linux-2.6.11-final-V0.7.40-00/fs/jbd/journal.c
> --- linux-2.6.11-final-V0.7.40-00.orig/fs/jbd/journal.c	2005-03-02 02:37:49.000000000 -0500
> +++ linux-2.6.11-final-V0.7.40-00/fs/jbd/journal.c	2005-03-16 07:47:50.000000000 -0500
> @@ -82,6 +82,9 @@
>
>  static int journal_convert_superblock_v1(journal_t *, journal_superblock_t *);
>
> +spinlock_t jbd_state_lock = SPIN_LOCK_UNLOCKED;
> +spinlock_t jbd_journal_lock = SPIN_LOCK_UNLOCKED;
> +
>  /*
>   * Helper function used to manage commit timeouts
>   */
> diff -ur linux-2.6.11-final-V0.7.40-00.orig/include/linux/jbd.h linux-2.6.11-final-V0.7.40-00/include/linux/jbd.h
> --- linux-2.6.11-final-V0.7.40-00.orig/include/linux/jbd.h	2005-03-02 02:38:19.000000000 -0500
> +++ linux-2.6.11-final-V0.7.40-00/include/linux/jbd.h	2005-03-16 08:51:27.292105187 -0500
> @@ -313,6 +313,8 @@
>  BUFFER_FNS(RevokeValid, revokevalid)
>  TAS_BUFFER_FNS(RevokeValid, revokevalid)
>  BUFFER_FNS(Freed, freed)
> +BUFFER_FNS(State,state)
> +BUFFER_FNS(JournalHead,journal)
>
>  static inline struct buffer_head *jh2bh(struct journal_head *jh)
>  {
> @@ -324,34 +326,50 @@
>  	return bh->b_private;
>  }
>
> +extern spinlock_t jbd_state_lock;
> +extern spinlock_t jbd_journal_lock;
> +
>  static inline void jbd_lock_bh_state(struct buffer_head *bh)
>  {
> -	bit_spin_lock(BH_State, &bh->b_state);
> +	spin_lock(&jbd_state_lock);
> +	BUG_ON(buffer_state(bh));
> +	set_buffer_state(bh);
>  }
>
>  static inline int jbd_trylock_bh_state(struct buffer_head *bh)
>  {
> -	return bit_spin_trylock(BH_State, &bh->b_state);
> +	if (spin_trylock(&jbd_state_lock)) {
> +		BUG_ON(buffer_state(bh));
> +		set_buffer_state(bh);
> +		return 1;
> +	}
> +	return 0;
>  }
>
>  static inline int jbd_is_locked_bh_state(struct buffer_head *bh)
>  {
> -	return bit_spin_is_locked(BH_State, &bh->b_state);
> +	return buffer_state(bh); //spin_is_locked(&jbd_state_lock);
>  }
>
>  static inline void jbd_unlock_bh_state(struct buffer_head *bh)
>  {
> -	bit_spin_unlock(BH_State, &bh->b_state);
> +	BUG_ON(!buffer_state(bh));
> +	clear_buffer_state(bh);
> +	spin_unlock(&jbd_state_lock);
>  }
>
>  static inline void jbd_lock_bh_journal_head(struct buffer_head *bh)
>  {
> -	bit_spin_lock(BH_JournalHead, &bh->b_state);
> +	spin_lock(&jbd_journal_lock);
> +	BUG_ON(buffer_journal(bh));
> +	set_buffer_journal(bh);
>  }
>
>  static inline void jbd_unlock_bh_journal_head(struct buffer_head *bh)
>  {
> -	bit_spin_unlock(BH_JournalHead, &bh->b_state);
> +	BUG_ON(!buffer_journal(bh));
> +	clear_buffer_journal(bh);
> +	spin_unlock(&jbd_journal_lock);
>  }
>
>  struct jbd_revoke_table_s;
> -
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