On 6/21/23 23:54, Richard W.M. Jones wrote:
> OCaml 5 is stricter than earlier versions about correct locking.
>
> We must release the OCaml runtime lock when calling nbd_close since it
> may do some long-running operations and we want to allow concurrent
> threads to run.
>
> However specifically if there are callbacks (eg. a debug callback)
> then we would end up trying to re-acquire the lock in the callback,
> resulting in a crash:
Drop the word "However"?
Paragraph #3 appears to support paragraph #2, not to oppose it.
Acked-by: Laszlo Ersek <ler...@redhat.com>
Laszlo
>
> (gdb) bt
> #0 __pthread_kill_implementation (threadid=<optimized out>,
> signo=signo@entry=6, no_tid=no_tid@entry=0) at pthread_kill.c:44
> #1 0x00007f47ffc8f773 in __pthread_kill_internal (signo=6,
> threadid=<optimized out>) at pthread_kill.c:78
> #2 0x00007f47ffc3e71e in __GI_raise (sig=sig@entry=6)
> at ../sysdeps/posix/raise.c:26
> #3 0x00007f47ffc2687f in __GI_abort () at abort.c:79
> #4 0x0000560c9eb62779 in caml_fatal_error ()
> #5 0x0000560c9eb63238 in caml_plat_fatal_error ()
> #6 0x0000560c9eb4ea77 in caml_acquire_domain_lock ()
> #7 0x0000560c9eb65cdc in caml_leave_blocking_section ()
> #8 0x0000560c9eaf8a87 in debug_wrapper (user_data=0x560ca0af2670,
> context=0x7f47fff8ca60 "nbd_close", msg=0x560ca0af28b0 "closing handle")
> at ../nbd-c.c:187
> #9 0x00007f47fff7072f in nbd_internal_debug (h=h@entry=0x560ca0b57db0,
> context=0x7f47fff8ca60 "nbd_close", context@entry=0x0,
> fs=fs@entry=0x7f47fff8ca6a "closing handle")
> at /home/rjones/d/libnbd/lib/debug.c:90
> #10 0x00007f47fff73f23 in nbd_close (h=0x560ca0b57db0)
> at /home/rjones/d/libnbd/lib/handle.c:127
> #11 0x0000560c9eae8dbe in nbd_internal_ocaml_handle_finalize (
> hv=<optimized out>) at ../handle.c:39
> #12 nbd_internal_ocaml_nbd_close (hv=<optimized out>) at ../handle.c:62
> #13 <signal handler called>
> #14 0x0000560c9eae84dc in camlTest_140_explicit_close__entry () at
> NBD.ml:148
> #15 0x0000560c9eae5c5b in caml_program ()
> #16 <signal handler called>
> #17 0x0000560c9eb6cb77 in caml_startup_common ()
> #18 0x0000560c9eb6cbef in caml_main ()
> #19 0x0000560c9eae5910 in main ()
> ---
> ocaml/handle.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/ocaml/handle.c b/ocaml/handle.c
> index fb45b30102..b3e5a0fc33 100644
> --- a/ocaml/handle.c
> +++ b/ocaml/handle.c
> @@ -26,6 +26,7 @@
> #include <caml/fail.h>
> #include <caml/memory.h>
> #include <caml/mlvalues.h>
> +#include <caml/threads.h>
>
> #include <libnbd.h>
>
> @@ -36,7 +37,9 @@ nbd_internal_ocaml_handle_finalize (value hv)
> {
> struct nbd_handle *h = NBD_val (hv);
>
> + caml_enter_blocking_section ();
> nbd_close (h);
> + caml_leave_blocking_section ();
> }
>
> value
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