[v1] block: Some multi-threading fixes

[PATCH 09/16] block/io: Take reqs_lock for tracked_requests

Hanna Czenczek posted 16 patches 2 weeks, 3 days ago

Diff against v2
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Maintainers: Paolo Bonzini <pbonzini@redhat.com>, "Alex Bennée" <alex.bennee@linaro.org>, Kevin Wolf <kwolf@redhat.com>, Hanna Reitz <hreitz@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, Fam Zheng <fam@euphon.net>, Ronnie Sahlberg <ronniesahlberg@gmail.com>, Peter Lieven <pl@dlhnet.de>, "Philippe Mathieu-Daudé" <philmd@linaro.org>, Ilya Dryomov <idryomov@gmail.com>, "Richard W.M. Jones" <rjones@redhat.com>, Stefan Weil <sw@weilnetz.de>

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[PATCH 09/16] block/io: Take reqs_lock for tracked_requests

Posted by Hanna Czenczek 2 weeks, 3 days ago

bdrv_co_get_self_request() does not take a lock around iterating through
bs->tracked_requests.  With multiqueue, it may thus iterate over a list
that is in the process of being modified, producing an assertion
failure:

../block/file-posix.c:3702: raw_do_pwrite_zeroes: Assertion `req' failed.

[0] abort() at /lib64/libc.so.6
[1] __assert_fail_base.cold() at /lib64/libc.so.6
[2] raw_do_pwrite_zeroes() at ../block/file-posix.c:3702
[3] bdrv_co_do_pwrite_zeroes() at ../block/io.c:1910
[4] bdrv_aligned_pwritev() at ../block/io.c:2109
[5] bdrv_co_do_zero_pwritev() at ../block/io.c:2192
[6] bdrv_co_pwritev_part() at ../block/io.c:2292
[7] bdrv_co_pwritev() at ../block/io.c:2225
[8] handle_alloc_space() at ../block/qcow2.c:2573
[9] qcow2_co_pwritev_task() at ../block/qcow2.c:2625

Fix this by taking reqs_lock.

Cc: qemu-stable@nongnu.org
Signed-off-by: Hanna Czenczek <hreitz@redhat.com>
---
 block/io.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/block/io.c b/block/io.c
index 9bd8ba8431..37df1e0253 100644
--- a/block/io.c
+++ b/block/io.c
@@ -721,11 +721,14 @@ BdrvTrackedRequest *coroutine_fn bdrv_co_get_self_request(BlockDriverState *bs)
     Coroutine *self = qemu_coroutine_self();
     IO_CODE();
 
+    qemu_mutex_lock(&bs->reqs_lock);
     QLIST_FOREACH(req, &bs->tracked_requests, list) {
         if (req->co == self) {
+            qemu_mutex_unlock(&bs->reqs_lock);
             return req;
         }
     }
+    qemu_mutex_unlock(&bs->reqs_lock);
 
     return NULL;
 }
-- 
2.51.0