I've found that NFS access to an exported tmpfs file system hangs indefinitely when the client first performs a GETATTR. The hanging nfsd thread is waiting for the inode lock in shmem_getattr():
task:nfsd state:D stack:0 pid:1775 tgid:1775 ppid:2 flags:0x00004000 Call Trace: <TASK> __schedule+0x770/0x7b0 schedule+0x33/0x50 schedule_preempt_disabled+0x19/0x30 rwsem_down_read_slowpath+0x206/0x230 down_read+0x3f/0x60 shmem_getattr+0x84/0xf0 vfs_getattr_nosec+0x9e/0xc0 vfs_getattr+0x49/0x50 fh_getattr+0x43/0x50 [nfsd] fh_fill_pre_attrs+0x4e/0xd0 [nfsd] nfsd4_open+0x51f/0x910 [nfsd] nfsd4_proc_compound+0x492/0x5d0 [nfsd] nfsd_dispatch+0x117/0x1f0 [nfsd] svc_process_common+0x3b2/0x5e0 [sunrpc] ? __pfx_nfsd_dispatch+0x10/0x10 [nfsd] svc_process+0xcf/0x130 [sunrpc] svc_recv+0x64e/0x750 [sunrpc] ? __wake_up_bit+0x4b/0x60 ? __pfx_nfsd+0x10/0x10 [nfsd] nfsd+0xc6/0xf0 [nfsd] kthread+0xed/0x100 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x2e/0x50 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 </TASK>
I bisected the problem to:
d949d1d14fa281ace388b1de978e8f2cd52875cf is the first bad commit commit d949d1d14fa281ace388b1de978e8f2cd52875cf Author: Jeongjun Park aha310510@gmail.com AuthorDate: Mon Sep 9 21:35:58 2024 +0900 Commit: Andrew Morton akpm@linux-foundation.org CommitDate: Mon Oct 28 21:40:39 2024 -0700
mm: shmem: fix data-race in shmem_getattr()
...
Link: https://lkml.kernel.org/r/20240909123558.70229-1-aha310510@gmail.com Fixes: 44a30220bc0a ("shmem: recalculate file inode when fstat") Signed-off-by: Jeongjun Park aha310510@gmail.com Reported-by: syzbot syzkaller@googlegroup.com Cc: Hugh Dickins hughd@google.com Cc: Yu Zhao yuzhao@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org
which first appeared in v6.12-rc6, and adds the line that is waiting on the inode lock when my NFS server hangs.
I haven't yet found the process that is holding the inode lock for this inode.
Because this commit addresses only a KCSAN splat that has been present since v4.3, and does not address a reported behavioral issue, I respectfully request that this commit be reverted immediately so that it does not appear in v6.12 final. Troubleshooting and testing should continue until a fix to the KCSAN issue can be found that does not deadlock NFS exports of tmpfs.