Prompt Title: NFS Process Wait Diagnosis

Human: PID: 1167904 TASK: ffff92a921c20000 CPU: 0 COMMAND: "sh" #0 [fffface29dd4b6d0] __schedule at ffffffffb4d49184 #1 [fffface29dd4b730] schedule at ffffffffb4d495f8 #2 [fffface29dd4b740] rpc_wait_bit_killable at ffffffffc071b2ce [sunrpc] #3 [fffface29dd4b758] __wait_on_bit at ffffffffb4d49aac #4 [fffface29dd4b790] out_of_line_wait_on_bit at ffffffffb4d49b51 #5 [fffface29dd4b7e0] __rpc_execute at ffffffffc071db7c [sunrpc] #6 [fffface29dd4b838] rpc_execute at ffffffffc07241f6 [sunrpc] #7 [fffface29dd4b858] rpc_run_task at ffffffffc070fcd4 [sunrpc] #8 [fffface29dd4b898] nfs4_call_sync_custom at ffffffffc090717b [nfsv4] #9 [fffface29dd4b8a8] nfs4_do_call_sync at ffffffffc0907209 [nfsv4] #10 [fffface29dd4b918] _nfs4_proc_getattr at ffffffffc0909f29 [nfsv4] #11 [fffface29dd4b9d8] nfs4_proc_getattr at ffffffffc091281a [nfsv4] #12 [fffface29dd4ba48] __nfs_revalidate_inode at ffffffffc0875b37 [nfs] #13 [fffface29dd4ba78] nfs_access_get_cached at ffffffffc086eb70 [nfs] #14 [fffface29dd4bac0] nfs_do_access at ffffffffc086ec80 [nfs] #15 [fffface29dd4bb48] nfs_permission at ffffffffc086ef4e [nfs] #16 [fffface29dd4bb68] inode_permission at ffffffffb47258d6 #17 [fffface29dd4bb90] link_path_walk at ffffffffb4725f92 #18 [fffface29dd4bbf0] path_openat at ffffffffb47283eb #19 [fffface29dd4bcc8] do_filp_open at ffffffffb472abe3 #20 [fffface29dd4bdd8] do_sys_open at ffffffffb4715854 #21 [fffface29dd4be30] tmhook_invoke at ffffffffc0d128fa [tmhook] #22 [fffface29dd4be68] tmhook_handler at ffffffffc0d12d13 [tmhook] #23 [fffface29dd4bf28] do_syscall_64 at ffffffffb440420b #24 [fffface29dd4bf50] entry_SYSCALL_64_after_hwframe at ffffffffb4e000ad

ChatGPT:

This is a stack trace, a list of function calls that were executed leading up to a particular point in a program. The information here indicates that the process with ID 1167904, running the "sh" command, was executing on CPU 0 and was interrupted by the scheduler. The process was waiting on a bit (bit 0) in the kernel's wait queue, which is used to synchronize access to shared resources. The process was waiting for an RPC (Remote Procedure Call) to complete, specifically a call to "nfs4_proc_getattr" to retrieve attributes for a file on an NFS (Network File System) server. The stack trace indicates that the process was waiting for this RPC to complete by executing the "__wait_on_bit" function. The functions listed above "__wait_on_bit" in the stack trace are the ones that called it, in reverse order. These functions were likely involved in setting up the RPC call or handling its response.

Human: what "entry_SYSCALL_64_after_hwframe" doing above stack trace

ChatGPT:

"entry_SYSCALL_64_after_hwframe" is the bottom-most function in the stack trace, and it is not part of the process that was interrupted by the scheduler. Instead, it is the entry point for system calls in the Linux kernel. When a process executes a system call, it triggers a software interrupt (syscall) that transfers control to the kernel. The kernel then executes the system call and returns control to the process. "entry_SYSCALL_64_after_hwframe" is the function that is called after the kernel has set up the hardware frame for the syscall and is about to execute the system call. It is part of the kernel's syscall handling mechanism and is not related to the specific process or its execution context.