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Subject: Re: [PATCH] nfs: Fix bdi handling for cloned superblocks
To: Jan Kara <jack@suse.cz>
References: <20170504070242.31501-1-jack@suse.cz>
Cc: linux-block@vger.kernel.org, linux-nfs@vger.kernel.org,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Trond Myklebust <trond.myklebust@primarydata.com>,
        Corentin Labbe <clabbe.montjoie@gmail.com>
From: Jens Axboe <axboe@kernel.dk>
Message-ID: <289c8d37-a292-2701-b03b-250f904fd022@kernel.dk>
Date: Thu, 4 May 2017 07:58:06 -0600
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In-Reply-To: <20170504070242.31501-1-jack@suse.cz>
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Sender: linux-nfs-owner@vger.kernel.org
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On 05/04/2017 01:02 AM, Jan Kara wrote:
> In commit 0d3b12584972 "nfs: Convert to separately allocated bdi" I have
> wrongly cloned bdi reference in nfs_clone_super(). Further inspection
> has shown that originally the code was actually allocating a new bdi (in
> ->clone_server callback) which was later registered in
> nfs_fs_mount_common() and used for sb->s_bdi in nfs_initialise_sb().
> This could later result in bdi for the original superblock not getting
> unregistered when that superblock got shutdown (as the cloned sb still
> held bdi reference) and later when a new superblock was created under
> the same anonymous device number, a clash in sysfs has happened on bdi
> registration:
> 
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 10284 at /linux-next/fs/sysfs/dir.c:31 sysfs_warn_dup+0x64/0x74
> sysfs: cannot create duplicate filename '/devices/virtual/bdi/0:32'
> Modules linked in: axp20x_usb_power gpio_axp209 nvmem_sunxi_sid sun4i_dma sun4i_ss virt_dma
> CPU: 1 PID: 10284 Comm: mount.nfs Not tainted 4.11.0-rc4+ #14
> Hardware name: Allwinner sun7i (A20) Family
> [<c010f19c>] (unwind_backtrace) from [<c010bc74>] (show_stack+0x10/0x14)
> [<c010bc74>] (show_stack) from [<c03c6e24>] (dump_stack+0x78/0x8c)
> [<c03c6e24>] (dump_stack) from [<c0122200>] (__warn+0xe8/0x100)
> [<c0122200>] (__warn) from [<c0122250>] (warn_slowpath_fmt+0x38/0x48)
> [<c0122250>] (warn_slowpath_fmt) from [<c02ac178>] (sysfs_warn_dup+0x64/0x74)
> [<c02ac178>] (sysfs_warn_dup) from [<c02ac254>] (sysfs_create_dir_ns+0x84/0x94)
> [<c02ac254>] (sysfs_create_dir_ns) from [<c03c8b8c>] (kobject_add_internal+0x9c/0x2ec)
> [<c03c8b8c>] (kobject_add_internal) from [<c03c8e24>] (kobject_add+0x48/0x98)
> [<c03c8e24>] (kobject_add) from [<c048d75c>] (device_add+0xe4/0x5a0)
> [<c048d75c>] (device_add) from [<c048ddb4>] (device_create_groups_vargs+0xac/0xbc)
> [<c048ddb4>] (device_create_groups_vargs) from [<c048dde4>] (device_create_vargs+0x20/0x28)
> [<c048dde4>] (device_create_vargs) from [<c02075c8>] (bdi_register_va+0x44/0xfc)
> [<c02075c8>] (bdi_register_va) from [<c023d378>] (super_setup_bdi_name+0x48/0xa4)
> [<c023d378>] (super_setup_bdi_name) from [<c0312ef4>] (nfs_fill_super+0x1a4/0x204)
> [<c0312ef4>] (nfs_fill_super) from [<c03133f0>] (nfs_fs_mount_common+0x140/0x1e8)
> [<c03133f0>] (nfs_fs_mount_common) from [<c03335cc>] (nfs4_remote_mount+0x50/0x58)
> [<c03335cc>] (nfs4_remote_mount) from [<c023ef98>] (mount_fs+0x14/0xa4)
> [<c023ef98>] (mount_fs) from [<c025cba0>] (vfs_kern_mount+0x54/0x128)
> [<c025cba0>] (vfs_kern_mount) from [<c033352c>] (nfs_do_root_mount+0x80/0xa0)
> [<c033352c>] (nfs_do_root_mount) from [<c0333818>] (nfs4_try_mount+0x28/0x3c)
> [<c0333818>] (nfs4_try_mount) from [<c0313874>] (nfs_fs_mount+0x2cc/0x8c4)
> [<c0313874>] (nfs_fs_mount) from [<c023ef98>] (mount_fs+0x14/0xa4)
> [<c023ef98>] (mount_fs) from [<c025cba0>] (vfs_kern_mount+0x54/0x128)
> [<c025cba0>] (vfs_kern_mount) from [<c02600f0>] (do_mount+0x158/0xc7c)
> [<c02600f0>] (do_mount) from [<c0260f98>] (SyS_mount+0x8c/0xb4)
> [<c0260f98>] (SyS_mount) from [<c0107840>] (ret_fast_syscall+0x0/0x3c)
> 
> Fix the problem by always creating new bdi for a superblock as we used
> to do.
> 
> Reported-and-tested-by: Corentin Labbe <clabbe.montjoie@gmail.com>
> Fixes: 0d3b12584972ce5781179ad3f15cca3cdb5cae05
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>  fs/nfs/internal.h |  6 +++---
>  fs/nfs/super.c    | 28 ++++++++++------------------
>  2 files changed, 13 insertions(+), 21 deletions(-)
> 
> Hi Jens,
> 
> can you please merge this fix to my series converting BDI handling in
> filesystems? Thanks!

Yep, added for a later pull in this merge window. Thanks Jan.

-- 
Jens Axboe