Misc rqspinlock updates #6248
Closed
Misc rqspinlock updates #6248
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
|
Upstream branch: 54c134f |
kernel-patches-daemon-bpf-rc
bot
force-pushed
the
bpf-next_base
branch
from
b8a9697 to
0ff1d70
Compare
|
Upstream branch: e2e668b |
Disable propagation and unwinding of the waiter queue in case the head waiter detects a deadlock condition, but keep it enabled in case of the timeout fallback. Currently, when the head waiter experiences an AA deadlock, it will signal all its successors in the queue to exit with an error. This is not ideal for cases where the same lock is held in contexts which can cause errors in an unrestricted fashion (e.g., BPF programs, or kernel paths invoked through BPF programs), and core kernel logic which is written in a correct fashion and does not expect deadlocks. The same reasoning can be extended to ABBA situations. Depending on the actual runtime schedule, one or both of the head waiters involved in an ABBA situation can detect and exit directly without terminating their waiter queue. If the ABBA situation manifests again, the waiters will keep exiting until progress can be made, or a timeout is triggered in case of more complicated locking dependencies. We still preserve the queue destruction in case of timeouts, as either the locking dependencies are too complex to be captured by AA and ABBA heuristics, or the owner is perpetually stuck. As such, it would be unwise to continue to apply the timeout for each new head waiter without terminating the queue, since we may end up waiting for more than 250 ms in aggregate with all participants in the locking transaction. The patch itself is fairly simple; we can simply signal our successor to become the next head waiter, and leave the queue without attempting to acquire the lock. With this change, the behavior for waiters in case of deadlocks experienced by a predecessor changes. It is guaranteed that call sites will no longer receive errors if the predecessors encounter deadlocks and the successors do not participate in one. This should lower the failure rate for waiters that are not doing improper locking opreations, just because they were unlucky to queue behind a misbehaving waiter. However, timeouts are still a possibility, hence they must be accounted for, so users cannot rely upon errors not occuring at all. Suggested-by: Amery Hung <[email protected]> Suggested-by: Alexei Starovoitov <[email protected]> Signed-off-by: Kumar Kartikeya Dwivedi <[email protected]>
Introduce a new mode for the rqspinlock stress test that exercises a deadlock that won't be detected by the AA and ABBA checks, such that we always reliably trigger the timeout fallback. We need 4 CPUs for this particular case, as CPU 0 is untouched, and three participant CPUs for triggering the ABBCCA case. Refactor the lock acquisition paths in the module to better reflect the three modes and choose the right lock depending on the context. Also drop ABBA case from running by default as part of test progs, since the stress test can consume a significant amount of time. Acked-by: Eduard Zingerman <[email protected]> Reviewed-by: Amery Hung <[email protected]> Signed-off-by: Kumar Kartikeya Dwivedi <[email protected]>
kernel-patches-daemon-bpf-rc
bot
force-pushed
the
series/1017405=>bpf-next
branch
from
77abf6c to
46bc40e
Compare
kernel-patches-daemon-bpf-rc
bot
force-pushed
the
bpf-next_base
branch
from
0ff1d70 to
75ba762
Compare
|
At least one diff in series https://patchwork.kernel.org/project/netdevbpf/list/?series=1017405 irrelevant now. Closing PR. |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Pull request for series with
subject: Misc rqspinlock updates
version: 1
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1017405