File 9pfs-fix-crash-in-v9fs_walk.patch of Package qemu

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File 9pfs-fix-crash-in-v9fs_walk.patch of Package qemu (Revision a94f3d7d94acf732c444a7381ceb42a4)

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From: Christian Schoenebeck <qemu_oss@crudebyte.com>
Date: Wed, 1 Sep 2021 18:15:10 +0200
Subject: 9pfs: fix crash in v9fs_walk()

Git-commit: f83df00900816476cca41bb536e4d532b297d76e

v9fs_walk() utilizes the v9fs_co_run_in_worker({...}) macro to run the
supplied fs driver code block on a background worker thread.

When either the 'Twalk' client request was interrupted or if the client
requested fid for that 'Twalk' request caused a stat error then that
fs driver code block was left by 'break' keyword, with the intention to
return from worker thread back to main thread as well:

v9fs_co_run_in_worker({
        if (v9fs_request_cancelled(pdu)) {
            err = -EINTR;
            break;
        }
        err = s->ops->lstat(&s->ctx, &dpath, &fidst);
        if (err < 0) {
            err = -errno;
            break;
        }
        ...
    });

However that 'break;' statement also skipped the v9fs_co_run_in_worker()
macro's final and mandatory

/* re-enter back to qemu thread */
    qemu_coroutine_yield();

call and thus caused the rest of v9fs_walk() to be continued being
executed on the worker thread instead of main thread, eventually
leading to a crash in the transport virtio transport driver.

To fix this issue and to prevent the same error from happening again by
other users of v9fs_co_run_in_worker() in future, auto wrap the supplied
code block into its own

do { } while (0);

loop inside the 'v9fs_co_run_in_worker' macro definition.

Full discussion and backtrace:
https://lists.gnu.org/archive/html/qemu-devel/2021-08/msg05209.html
https://lists.gnu.org/archive/html/qemu-devel/2021-09/msg00174.html

Fixes: 8d6cb100731c4d28535adbf2a3c2d1f29be3fef4
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Cc: qemu-stable@nongnu.org
Reviewed-by: Greg Kurz <groug@kaod.org>
Message-Id: <E1mLTBg-0002Bh-2D@lizzy.crudebyte.com>
Signed-off-by: Jose R. Ziviani <jziviani@suse.de>
---
 hw/9pfs/coth.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/hw/9pfs/coth.h b/hw/9pfs/coth.h
index c51289903d0df0ff65f9d3f2649b..f83c7dda7bb8df8295c6a6db59c5 100644
--- a/hw/9pfs/coth.h
+++ b/hw/9pfs/coth.h
@@ -51,7 +51,9 @@
          */                                                             \
         qemu_coroutine_yield();                                         \
         qemu_bh_delete(co_bh);                                          \
-        code_block;                                                     \
+        do {                                                            \
+            code_block;                                                 \
+        } while (0);                                                    \
         /* re-enter back to qemu thread */                              \
         qemu_coroutine_yield();                                         \
     } while (0)

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File 9pfs-fix-crash-in-v9fs_walk.patch of Package qemu (Revision a94f3d7d94acf732c444a7381ceb42a4)

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