** Changed in: linux-aws (Ubuntu Focal)
Status: New => Fix Committed
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https://bugs.launchpad.net/bugs/1926184
Title:
locking/qrwlock: Fix ordering in queued_write_lock_slowpath()
Status in linux package in Ubuntu:
In Progress
Status in linux-aws package in Ubuntu:
In Progress
Status in linux source package in Bionic:
New
Status in linux-aws source package in Bionic:
Fix Committed
Status in linux source package in Focal:
New
Status in linux-aws source package in Focal:
Fix Committed
Status in linux source package in Groovy:
New
Status in linux-aws source package in Groovy:
New
Status in linux source package in Hirsute:
New
Status in linux-aws source package in Hirsute:
New
Bug description:
[Impact]
* Out of order reads can fetch a NULL pointer causing a kernel crash. Affects
kernels from v4.15 to v5.11.
[Fix]
* commit 84a24bf8c52e ("locking/qrwlock: Fix ordering in
queued_write_lock_slowpath()")
* For Bionic, we also require an additional patch: commit fcfdfe30e324
("locking/barriers: Introduce smp_cond_load_relaxed() and
atomic_cond_read_relaxed()")
[Where problems could occur]
* This is quite a subtle bug. It is more prevalent on arm64. Regression
possibility seems quite low. The worst impact could be a minor performance
degradation.
* Kernels 4.15 / 5.4 / 5.8 / 5.11 were successfully built and booted
with this patch. Also, by using ftrace we could see that the changed
function was executed with success multiple times.
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