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74 lines
2.4 KiB
74 lines
2.4 KiB
From e42cd859265c34d2013a45b742d4c36bb7617445 Mon Sep 17 00:00:00 2001
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From: "Richard W.M. Jones" <rjones@redhat.com>
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Date: Tue, 27 Jun 2023 12:09:12 +0100
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Subject: [PATCH] ocaml: Conditionally acquire the lock in callbacks
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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This fix was originally suggested by Jürgen Hötzel (link below) which
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I have lightly modified so it works with OCaml <= 4 too.
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Link: https://listman.redhat.com/archives/libguestfs/2023-May/031640.html
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Link: https://discuss.ocaml.org/t/test-caml-state-and-conditionally-caml-acquire-runtime-system-good-or-bad/12489
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(cherry picked from commit 16464878cf980ffab1c1aeada2e438b0281ad1bc)
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---
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ocaml/guestfs-c.c | 25 +++++++++++++++++++++++--
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1 file changed, 23 insertions(+), 2 deletions(-)
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diff --git a/ocaml/guestfs-c.c b/ocaml/guestfs-c.c
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index a1865a72..67dc3547 100644
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--- a/ocaml/guestfs-c.c
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+++ b/ocaml/guestfs-c.c
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@@ -19,6 +19,7 @@
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#include <config.h>
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#include <stdio.h>
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#include <stdlib.h>
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+#include <stdbool.h>
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#include <string.h>
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#include <errno.h>
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@@ -36,6 +37,7 @@
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#include <caml/signals.h>
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#include <caml/threads.h>
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#include <caml/unixsupport.h>
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+#include <caml/version.h>
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#include "guestfs-c.h"
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@@ -397,13 +399,32 @@ event_callback_wrapper (guestfs_h *g,
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{
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/* Ensure we are holding the GC lock before any GC operations are
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* possible. (RHBZ#725824)
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+ *
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+ * There are many paths where we already hold the OCaml lock before
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+ * this function, for example "non-blocking" calls, and the
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+ * libguestfs global atexit path (which calls guestfs_close). To
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+ * avoid double acquisition we need to check if we already hold the
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+ * lock. OCaml 5 is strict about this. In earlier OCaml versions
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+ * there is no way to check, but they did not implement the lock as
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+ * a mutex and so it didn't cause problems.
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+ *
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+ * See also:
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+ * https://discuss.ocaml.org/t/test-caml-state-and-conditionally-caml-acquire-runtime-system-good-or-bad/12489
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*/
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- caml_acquire_runtime_system ();
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+#if OCAML_VERSION_MAJOR >= 5
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+ bool acquired = caml_state != NULL;
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+#else
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+ const bool acquired = false;
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+#endif
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+
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+ if (!acquired)
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+ caml_acquire_runtime_system ();
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event_callback_wrapper_locked (g, data, event, event_handle, flags,
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buf, buf_len, array, array_len);
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- caml_release_runtime_system ();
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+ if (!acquired)
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+ caml_release_runtime_system ();
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}
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value
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