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Date: Tue, 14 Jun 2022 16:29:55 +0200
From: Jan Kara <jack@...e.cz>
To: Suzuki K Poulose <suzuki.poulose@....com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, stable@...r.kernel.org,
Jchao Sun <sunjunchao2870@...il.com>, Jan Kara <jack@...e.cz>
Subject: Re: [PATCH] writeback: Avoid grabbing the wb if the we don't add it
to dirty list
On Tue 14-06-22 13:46:18, Suzuki K Poulose wrote:
> Commit 10e14073107d moved grabbing the wb for an inode early enough,
> skipping the checks whether if this inode needs to be really added
> to the dirty list (backed by blockdev or unhashed inode). This causes
> a crash with kdevtmpfs as below, on an arm64 Juno board, as below:
>
> [ 1.446493] printk: console [ttyAMA0] printing thread started
> [ 1.447195] printk: bootconsole [pl11] printing thread stopped
> [ 1.467193] Unable to handle kernel paging request at virtual address ffff800871242000
> [ 1.467793] Mem abort info:
> [ 1.468093] ESR = 0x0000000096000005
> [ 1.468413] EC = 0x25: DABT (current EL), IL = 32 bits
> [ 1.468741] SET = 0, FnV = 0
> [ 1.469093] EA = 0, S1PTW = 0
> [ 1.469396] FSC = 0x05: level 1 translation fault
> [ 1.470493] Data abort info:
> [ 1.470793] ISV = 0, ISS = 0x00000005
> [ 1.471093] CM = 0, WnR = 0
> [ 1.471444] swapper pgtable: 4k pages, 48-bit VAs, pgdp=0000000081c10000
> [ 1.471798] [ffff800871242000] pgd=10000008fffff003,
> p4d=10000008fffff003, pud=0000000000000000
> [ 1.472836] Internal error: Oops: 96000005 [#1] PREEMPT SMP
> [ 1.472918] Modules linked in:
> [ 1.473085] CPU: 1 PID: 35 Comm: kdevtmpfs Tainted: G T 5.19.0-rc1+ #49
> [ 1.473246] Hardware name: Foundation-v8A (DT)
> [ 1.473345] pstate: 40400009 (nZcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> [ 1.473493] pc : locked_inode_to_wb_and_lock_list+0xbc/0x2a4
> [ 1.473656] lr : locked_inode_to_wb_and_lock_list+0x8c/0x2a4
> [ 1.473820] sp : ffff80000b77bc10
> [ 1.473901] x29: ffff80000b77bc10 x28: 0000000000000001 x27: 0000000000000004
> [ 1.474193] x26: 0000000000000000 x25: ffff000800888600 x24: ffff0008008885e8
> [ 1.474393] x23: ffff80000848ddd4 x22: ffff80000a754f30 x21: ffff80000a7eaaf0
> [ 1.474693] x20: ffff000800888150 x19: ffff80000b6a4150 x18: ffff80000ac3ac00
> [ 1.474917] x17: 0000000070526bee x16: 000000003ac581ee x15: ffff80000ac42660
> [ 1.475195] x14: 0000000000000000 x13: 0000000000007a60 x12: 0000000000000002
> [ 1.475428] x11: ffff80000a7eaaf0 x10: 0000000000000004 x9 : 000000008845fe88
> [ 1.475622] x8 : ffff000800868000 x7 : ffff80000ab98000 x6 : 00000000114514e2
> [ 1.475893] x5 : 0000000000000000 x4 : 0000000000020019 x3 : 0000000000000001
> [ 1.476113] x2 : ffff800871242000 x1 : ffff800871242000 x0 : ffff000800868000
> [ 1.476393] Call trace:
> [ 1.476493] locked_inode_to_wb_and_lock_list+0xbc/0x2a4
> [ 1.476605] __mark_inode_dirty+0x3d8/0x6e0
> [ 1.476793] simple_setattr+0x5c/0x84
> [ 1.476933] notify_change+0x3ec/0x470
> [ 1.477096] handle_create+0x1b8/0x224
> [ 1.477193] devtmpfsd+0x98/0xf8
> [ 1.477342] kthread+0x124/0x130
> [ 1.477512] ret_from_fork+0x10/0x20
> [ 1.477670] Code: b9000802 d2800023 d53cd042 8b020021 (f823003f)
> [ 1.477793] ---[ end trace 0000000000000000 ]---
> [ 1.478093] note: kdevtmpfs[35] exited with preempt_count 2
>
> The problem was bisected to the above commit and moving the bail check
> early solves the problem for me.
>
> Fixes: 10e14073107d ("writeback: Fix inode->i_io_list not be protected by inode->i_lock error")
> CC: stable@...r.kernel.org
> Cc: Jchao Sun <sunjunchao2870@...il.com>
> Cc: Jan Kara <jack@...e.cz>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
Thanks for debugging this! The problem actually is not that we cannot call
locked_inode_to_wb_and_lock_list() for devtmpfs inode. The problem is that
we get called so early during boot that noop_backing_dev_info is not
initialized yet and that breaks the code. But I agree the quick fix for
this breakage is to exclude unhashed inodes early in __mark_inode_dirty().
I'll update the changelog and code comment (and cleanup the condition when
moving it) and push the result to my tree.
Honza
> ---
> fs/fs-writeback.c | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 05221366a16d..cf68114af68b 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -2416,6 +2416,14 @@ void __mark_inode_dirty(struct inode *inode, int flags)
> inode->i_state &= ~I_DIRTY_TIME;
> inode->i_state |= flags;
>
> + /*
> + * Only add valid (hashed) inodes to the superblock's
> + * dirty list. Add blockdev inodes as well.
> + */
> + if (!S_ISBLK(inode->i_mode)) {
> + if (inode_unhashed(inode))
> + goto out_unlock_inode;
> + }
> /*
> * Grab inode's wb early because it requires dropping i_lock and we
> * need to make sure following checks happen atomically with dirty
> @@ -2436,14 +2444,6 @@ void __mark_inode_dirty(struct inode *inode, int flags)
> if (inode->i_state & I_SYNC_QUEUED)
> goto out_unlock;
>
> - /*
> - * Only add valid (hashed) inodes to the superblock's
> - * dirty list. Add blockdev inodes as well.
> - */
> - if (!S_ISBLK(inode->i_mode)) {
> - if (inode_unhashed(inode))
> - goto out_unlock;
> - }
> if (inode->i_state & I_FREEING)
> goto out_unlock;
>
> --
> 2.35.3
>
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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