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author | Peter Xu <peterx@redhat.com> | 2022-10-04 14:24:27 -0400 |
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committer | Juan Quintela <quintela@redhat.com> | 2022-11-21 11:58:10 +0100 |
commit | f5816b5c86ed399c99ce8662a4ed96aab32c5eef (patch) | |
tree | 2201bf315e882ff1cd4d5c1f5784b19ec7efb8e9 /qga | |
parent | 4934a5dd7c68f5ab15f17498db4fc20ed6db9578 (diff) | |
download | qemu-f5816b5c86ed399c99ce8662a4ed96aab32c5eef.zip qemu-f5816b5c86ed399c99ce8662a4ed96aab32c5eef.tar.gz qemu-f5816b5c86ed399c99ce8662a4ed96aab32c5eef.tar.bz2 |
migration: Fix race on qemu_file_shutdown()
In qemu_file_shutdown(), there's a possible race if with current order of
operation. There're two major things to do:
(1) Do real shutdown() (e.g. shutdown() syscall on socket)
(2) Update qemufile's last_error
We must do (2) before (1) otherwise there can be a race condition like:
page receiver other thread
------------- ------------
qemu_get_buffer()
do shutdown()
returns 0 (buffer all zero)
(meanwhile we didn't check this retcode)
try to detect IO error
last_error==NULL, IO okay
install ALL-ZERO page
set last_error
--> guest crash!
To fix this, we can also check retval of qemu_get_buffer(), but not all
APIs can be properly checked and ultimately we still need to go back to
qemu_file_get_error(). E.g. qemu_get_byte() doesn't return error.
Maybe some day a rework of qemufile API is really needed, but for now keep
using qemu_file_get_error() and fix it by not allowing that race condition
to happen. Here shutdown() is indeed special because the last_error was
emulated. For real -EIO errors it'll always be set when e.g. sendmsg()
error triggers so we won't miss those ones, only shutdown() is a bit tricky
here.
Cc: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Diffstat (limited to 'qga')
0 files changed, 0 insertions, 0 deletions