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commitb613c7f314upstream. A non-first waiter can potentially spin in the for loop of rwsem_down_write_slowpath() without sleeping but fail to acquire the lock even if the rwsem is free if the following sequence happens: Non-first RT waiter First waiter Lock holder ------------------- ------------ ----------- Acquire wait_lock rwsem_try_write_lock(): Set handoff bit if RT or wait too long Set waiter->handoff_set Release wait_lock Acquire wait_lock Inherit waiter->handoff_set Release wait_lock Clear owner Release lock if (waiter.handoff_set) { rwsem_spin_on_owner((); if (OWNER_NULL) goto trylock_again; } trylock_again: Acquire wait_lock rwsem_try_write_lock(): if (first->handoff_set && (waiter != first)) return false; Release wait_lock A non-first waiter cannot really acquire the rwsem even if it mistakenly believes that it can spin on OWNER_NULL value. If that waiter happens to be an RT task running on the same CPU as the first waiter, it can block the first waiter from acquiring the rwsem leading to live lock. Fix this problem by making sure that a non-first waiter cannot spin in the slowpath loop without sleeping. Fixes:d257cc8cb8("locking/rwsem: Make handoff bit handling more consistent") Signed-off-by: Waiman Long <longman@redhat.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Tested-by: Mukesh Ojha <quic_mojha@quicinc.com> Reviewed-by: Mukesh Ojha <quic_mojha@quicinc.com> Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20230126003628.365092-2-longman@redhat.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.