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C API deadlock in hyper_executor::poll_next #3369
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This was referenced Oct 23, 2023
Wow, thanks so much for the write-up, and finding this deadlock! Fixing that up shouldn't be too complicated. |
seanmonstar
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Effort: easy. A task that would be a great starting point for a new contributor.
A-ffi
Area: ffi (C API)
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Oct 23, 2023
Oh, you even submitted a PR already, double thanks! |
seanmonstar
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Oct 23, 2023
poll_next locks the driver, and also calls drain_queue while holding that lock. Since drain_queue locks the driver too, that results in a deadlock. To fix, unlock the driver before calling drain_queue. Closes #3369
0xE282B0
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poll_next locks the driver, and also calls drain_queue while holding that lock. Since drain_queue locks the driver too, that results in a deadlock. To fix, unlock the driver before calling drain_queue. Closes hyperium#3369
. nvm |
0xE282B0
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poll_next locks the driver, and also calls drain_queue while holding that lock. Since drain_queue locks the driver too, that results in a deadlock. To fix, unlock the driver before calling drain_queue. Closes hyperium#3369 Signed-off-by: Sven Pfennig <s.pfennig@reply.de>
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Version: current master, dd638b5
Platform: Linux 6.2.0-34-generic #34-Ubuntu SMP PREEMPT_DYNAMIC Mon Sep 4 13:06:55 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
In curl/curl#11203 (comment), @marlonbaeten reported that removing
hyper_clientconn_free(client);
from curl's c-hyper code caused curl to never send the request.I did a little poking around and I believe what's happening is a deadlock. I'm not sure yet why freeing the client triggers the deadlock, but I can see in the Hyper code where it happens.
In hyper_executor::poll_next,
self.driver
is locked and thendrain_queue
is called :hyper/src/ffi/task.rs
Lines 129 to 134 in dd638b5
drain_queue
then tries to lockself.driver
a second time:hyper/src/ffi/task.rs
Lines 151 to 156 in dd638b5
The docs for Mutex::lock say:
Steps to reproduce:
Build Hyper's FFI library using this patch to add some println debugging lines:
Build curl against that version of Hyper's FFI library, using this patch against curl:
Observe this output, followed by a hang:
The text was updated successfully, but these errors were encountered: