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0f8821da48The MNT_WRITE_HOLD flag is used to hold back any new writers while the mount point is about to be made read-only. __mnt_want_write() then loops with disabled preemption until this flag disappears. Callers of mnt_hold_writers() (which sets the flag) hold the spinlock_t of mount_lock (seqlock_t) which disables preemption on !PREEMPT_RT and ensures the task is not scheduled away so that the spinning side spins for a long time. On PREEMPT_RT the spinlock_t does not disable preemption and so it is possible that the task setting MNT_WRITE_HOLD is preempted by task with higher priority which then spins infinitely waiting for MNT_WRITE_HOLD to get removed. Acquire mount_lock::lock which is held by setter of MNT_WRITE_HOLD. This will PI-boost the owner and wait until the lock is dropped and which means that MNT_WRITE_HOLD is cleared again. Link: https://lore.kernel.org/r/20211025152218.opvcqfku2lhqvp4o@linutronix.de Link: https://lore.kernel.org/r/20211125120711.dgbsienyrsxfzpoi@linutronix.de Acked-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> |
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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.