fix 'bad file descriptor' failures

pageserver/src/virtual_file.rs

@@ -16,7 +16,7 @@ use camino::{Utf8Path, Utf8PathBuf};
 use once_cell::sync::OnceCell;
 use std::fs::{self, File};
 use std::io::{Error, ErrorKind, Seek, SeekFrom};
-use std::os::fd::{AsRawFd, FromRawFd, OwnedFd, RawFd};
+use std::os::fd::{AsRawFd, FromRawFd, OwnedFd, RawFd, IntoRawFd};
 use std::os::unix::fs::FileExt;
 use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
 use tokio::sync::{RwLock, RwLockReadGuard, RwLockWriteGuard};
@@ -713,7 +713,9 @@ impl FileGuard {
         // - lifetime of the fd: `file` doesn't outlive the OwnedFd stored in `self`.
         // - `&` usage below: `self` is `&`, hence Rust typesystem guarantees there are is no `&mut`
         let file = unsafe { File::from_raw_fd(self.as_ref().as_raw_fd()) };
-        with(&file)
+        let res = with(&file);
+        let _ = file.into_raw_fd();
+        res
     }
     // TODO: switch to tokio-epoll-uring native operations.
     fn with_std_file_mut<F, R>(&mut self, with: F) -> R
@@ -724,7 +726,9 @@ impl FileGuard {
         // - lifetime of the fd: `file` doesn't outlive the OwnedFd stored in `self`.
         // - &mut usage below: `self` is `&mut`, hence this call is the only task/thread that has control over the underlying fd
         let mut file = unsafe { File::from_raw_fd(self.as_ref().as_raw_fd()) };
-        with(&mut file)
+        let res = with(&mut file);
+        let _ = file.into_raw_fd();
+        res
     }
 }