From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49563) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dACoZ-0000ax-Eq for qemu-devel@nongnu.org; Mon, 15 May 2017 06:01:20 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dACoU-0005tH-K1 for qemu-devel@nongnu.org; Mon, 15 May 2017 06:01:19 -0400 From: Paolo Bonzini Date: Mon, 15 May 2017 12:00:55 +0200 Message-Id: <20170515100059.15795-4-pbonzini@redhat.com> In-Reply-To: <20170515100059.15795-1-pbonzini@redhat.com> References: <20170515100059.15795-1-pbonzini@redhat.com> Subject: [Qemu-devel] [PATCH v3 3/7] curl: avoid recursive locking of BDRVCURLState mutex List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: jcody@redhat.com, rjones@redhat.com, qemu-block@nongnu.org, qemu-stable@nongnu.org The curl driver has a ugly hack where, if it cannot find an empty CURLState, it just uses aio_poll to wait for one to be empty. This is probably buggy when used together with dataplane, and the simplest way to fix it is to use coroutines instead. A more immediate effect of the bug however is that it can cause a recursive call to curl_readv_bh_cb and recursively taking the BDRVCURLState mutex. This causes a deadlock. The fix is to unlock the mutex around aio_poll, but for cleanliness we should also take the mutex around all calls to curl_init_state, even if reaching the unlock/lock pair is impossible. The same is true for curl_clean_state. Reported-by: Kun Wei Tested-by: Richard W.M. Jones Cc: qemu-stable@nongnu.org Cc: Jeff Cody Signed-off-by: Paolo Bonzini --- v2->v3: add missing qemu_mutex_destroy on failure case block/curl.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/block/curl.c b/block/curl.c index 924c2a2088..5e6ddf3a34 100644 --- a/block/curl.c +++ b/block/curl.c @@ -281,6 +281,7 @@ read_end: return size * nmemb; } +/* Called with s->mutex held. */ static int curl_find_buf(BDRVCURLState *s, size_t start, size_t len, CURLAIOCB *acb) { @@ -453,6 +454,7 @@ static void curl_multi_timeout_do(void *arg) #endif } +/* Called with s->mutex held. */ static CURLState *curl_init_state(BlockDriverState *bs, BDRVCURLState *s) { CURLState *state = NULL; @@ -471,7 +473,9 @@ static CURLState *curl_init_state(BlockDriverState *bs, BDRVCURLState *s) break; } if (!state) { + qemu_mutex_unlock(&s->mutex); aio_poll(bdrv_get_aio_context(bs), true); + qemu_mutex_lock(&s->mutex); } } while(!state); @@ -534,6 +538,7 @@ static CURLState *curl_init_state(BlockDriverState *bs, BDRVCURLState *s) return state; } +/* Called with s->mutex held. */ static void curl_clean_state(CURLState *s) { int j; @@ -565,6 +570,7 @@ static void curl_detach_aio_context(BlockDriverState *bs) BDRVCURLState *s = bs->opaque; int i; + qemu_mutex_lock(&s->mutex); for (i = 0; i < CURL_NUM_STATES; i++) { if (s->states[i].in_use) { curl_clean_state(&s->states[i]); @@ -580,6 +586,7 @@ static void curl_detach_aio_context(BlockDriverState *bs) curl_multi_cleanup(s->multi); s->multi = NULL; } + qemu_mutex_unlock(&s->mutex); timer_del(&s->timer); } @@ -677,6 +684,7 @@ static int curl_open(BlockDriverState *bs, QDict *options, int flags, return -EROFS; } + qemu_mutex_init(&s->mutex); opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort); qemu_opts_absorb_qdict(opts, options, &local_err); if (local_err) { @@ -747,7 +755,9 @@ static int curl_open(BlockDriverState *bs, QDict *options, int flags, DPRINTF("CURL: Opening %s\n", file); s->aio_context = bdrv_get_aio_context(bs); s->url = g_strdup(file); + qemu_mutex_lock(&s->mutex); state = curl_init_state(bs, s); + qemu_mutex_unlock(&s->mutex); if (!state) goto out_noclean; @@ -791,11 +801,12 @@ static int curl_open(BlockDriverState *bs, QDict *options, int flags, } DPRINTF("CURL: Size = %zd\n", s->len); + qemu_mutex_lock(&s->mutex); curl_clean_state(state); + qemu_mutex_unlock(&s->mutex); curl_easy_cleanup(state->curl); state->curl = NULL; - qemu_mutex_init(&s->mutex); curl_attach_aio_context(bs, bdrv_get_aio_context(bs)); qemu_opts_del(opts); @@ -806,6 +817,7 @@ out: curl_easy_cleanup(state->curl); state->curl = NULL; out_noclean: + qemu_mutex_destroy(&s->mutex); g_free(s->cookie); g_free(s->url); qemu_opts_del(opts); -- 2.12.2