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migration: Fix possible races when shutting down the return path 

We cannot call qemu_file_shutdown() on the return path file without
taking the file lock. The return path thread could be running it's
cleanup code and have just cleared the from_dst_file pointer.

Checking ms->to_dst_file for errors could also race with
migrate_fd_cleanup() which clears the to_dst_file pointer.

Protect both accesses by taking the file lock.

This was caught by inspection, it should be rare, but the next patches
will start calling this code from other places, so let's do the
correct thing.

Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20230918172822.19052-4-farosas@suse.de>
master
Fabiano Rosas 2023-09-18 14:28:17 -03:00 committed by Stefan Hajnoczi
parent 28a8347281
commit 639decf529
1 changed files with 10 additions and 9 deletions
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19
migration/migration.c
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@ -2064,17 +2064,18 @@ static int open_return_path_on_source(MigrationState *ms,
static int await_return_path_close_on_source(MigrationState *ms)
{
/*
* If this is a normal exit then the destination will send a SHUT and the
* rp_thread will exit, however if there's an error we need to cause
* it to exit.
* If this is a normal exit then the destination will send a SHUT
* and the rp_thread will exit, however if there's an error we
* need to cause it to exit. shutdown(2), if we have it, will
* cause it to unblock if it's stuck waiting for the destination.
*/
if (qemu_file_get_error(ms->to_dst_file) && ms->rp_state.from_dst_file) {
/*
* shutdown(2), if we have it, will cause it to unblock if it's stuck
* waiting for the destination.
*/
qemu_file_shutdown(ms->rp_state.from_dst_file);
WITH_QEMU_LOCK_GUARD(&ms->qemu_file_lock) {
if (ms->to_dst_file && ms->rp_state.from_dst_file &&
qemu_file_get_error(ms->to_dst_file)) {
qemu_file_shutdown(ms->rp_state.from_dst_file);
}
}
trace_await_return_path_close_on_source_joining();
qemu_thread_join(&ms->rp_state.rp_thread);
ms->rp_state.rp_thread_created = false;