Re: nfs hang bugs

[Chuck Lever III <chuck.lever@oracle.com>]

Hi!

> On Nov 11, 2021, at 11:39 AM, 程洋 <chengyang@xiaomi.com> wrote:
> 
> Hi. I'm an server engineer who hold gerrit servers. And uses nfs as my harddisk.
> Some time I found when I run `git pack-refs`, it will hang, and it causes deadlock in kernel, prevent other fs command to execute like `ls`
> Pretty much like this, but not the same issue.  https://about.gitlab.com/blog/2018/11/14/how-we-spent-two-weeks-hunting-an-nfs-bug/
> 
> Since I'm new to NFS, I don't know what else can I provide. If there anyway to get more debug information, please feel free to ask me.
> 
> My NFS server: Ubuntu 16.04
> My NFS client: Ubuntu 18.04

Just to note that this is a developer mailing list, not
really for user issues. For faster response, it's best
to work directly with your Linux distributor.

Your description sounds like a network or server issue:
the client looks like it's legitimately waiting for a
response rather than stuck somewhere unexpected.

Some other information for folks here to help out:
- Mount options on the client
- Server configuration and unusual log messages
- If you have a reproducer, you could post it here


> `git pack-refs strace`
> write(3, "users/94/1003094\n886741817c1d824"..., 8192) = 8192
> write(3, "ers/95/1006795\n7ec95f6ad772f6d63"..., 8192) = 8192
> write(3, "s/96/1011196\n5e310bf8491276a6a8d"..., 8192) = 8192
> write(3, "98/1000998\n3e1f177f0427e7aa79065"..., 8192) = 8192
> write(3, "/1004899\n14e572b05b3bb857d14d990"..., 3726) = 3726
> close(3)                                = 0
> access("hooks/reference-transaction", X_OK) = -1 ENOENT (No such file or directory)
> munmap(0x7f7c2ef5b000, 3903118)         = 0
> rename("/home/work/repositories/miui/All-Users.git/./packed-refs.new", "/home/work/repositories/miui/All-Users.git/./packed-refs"
> 
> `git pack-refs kernel stack`
> [<0>] rpc_wait_bit_killable+0x24/0xa0 [sunrpc]
> [<0>] __rpc_wait_for_completion_task+0x2d/0x30 [sunrpc]
> [<0>] nfs_rename+0xc5/0x310 [nfs]
> [<0>] vfs_rename+0x3dc/0xa80
> [<0>] do_renameat2+0x4ca/0x590
> [<0>] __x64_sys_rename+0x20/0x30
> [<0>] do_syscall_64+0x57/0x190
> [<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> 
> `ls` strace:
> ......
> .....
> mmap(NULL, 1683056, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f63251b0000
> close(3)                                = 0
> ioctl(1, TCGETS, {B38400 opost isig icanon echo ...}) = 0
> ioctl(1, TIOCGWINSZ, {ws_row=33, ws_col=113, ws_xpixel=0, ws_ypixel=0}) = 0
> openat(AT_FDCWD, ".", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = 3
> fstat(3, {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
> getdents(3
> 
> `ls kernel stack`:
> [<0>] rwsem_down_write_slowpath+0x23d/0x4c0
> [<0>] iterate_dir+0x126/0x1b0
> [<0>] __x64_sys_getdents+0xab/0x140
> [<0>] do_syscall_64+0x57/0x190
> [<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
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--
Chuck Lever