Kernel: Only lock process file descriptor table once in sys$poll()

Grab the OpenFileDescriptions mutex once and hold on to it while
populating the SelectBlocker::FDVector.

1 files changed, 17 insertions, 14 deletions

diff --git a/Kernel/Syscalls/poll.cpp b/Kernel/Syscalls/poll.cpp
index a783b72f4d..1ea55e2dad 100644
--- a/Kernel/Syscalls/poll.cpp
+++ b/Kernel/Syscalls/poll.cpp
@@ -47,20 +47,23 @@ ErrorOr<FlatPtr> Process::sys$poll(Userspace<const Syscall::SC_poll_params*> use
     Thread::SelectBlocker::FDVector fds_info;
     TRY(fds_info.try_ensure_capacity(params.nfds));
 
-    for (size_t i = 0; i < params.nfds; i++) {
-        auto& pfd = fds_copy[i];
-        auto description = TRY(m_fds.with_shared([&](auto& fds) { return fds.open_file_description(pfd.fd); }));
-        BlockFlags block_flags = BlockFlags::Exception; // always want POLLERR, POLLHUP, POLLNVAL
-        if (pfd.events & POLLIN)
-            block_flags |= BlockFlags::Read;
-        if (pfd.events & POLLOUT)
-            block_flags |= BlockFlags::Write;
-        if (pfd.events & POLLPRI)
-            block_flags |= BlockFlags::ReadPriority;
-        if (pfd.events & POLLWRBAND)
-            block_flags |= BlockFlags::WritePriority;
-        fds_info.unchecked_append({ move(description), block_flags });
-    }
+    TRY(m_fds.with_shared([&](auto& fds) -> ErrorOr<void> {
+        for (size_t i = 0; i < params.nfds; i++) {
+            auto& pfd = fds_copy[i];
+            auto description = TRY(fds.open_file_description(pfd.fd));
+            BlockFlags block_flags = BlockFlags::Exception; // always want POLLERR, POLLHUP, POLLNVAL
+            if (pfd.events & POLLIN)
+                block_flags |= BlockFlags::Read;
+            if (pfd.events & POLLOUT)
+                block_flags |= BlockFlags::Write;
+            if (pfd.events & POLLPRI)
+                block_flags |= BlockFlags::ReadPriority;
+            if (pfd.events & POLLWRBAND)
+                block_flags |= BlockFlags::WritePriority;
+            fds_info.unchecked_append({ move(description), block_flags });
+        }
+        return {};
+    }));
 
     auto* current_thread = Thread::current();