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Arnd Bergman reports: """ The conditional spinlock confuses gcc into thinking the 'flags' value might contain uninitialized data: drivers/gpu/drm/i915/i915_pmu.c: In function '__i915_pmu_event_read': arch/x86/include/asm/paravirt_types.h:573:3: error: 'flags' may be used uninitialized in this function [-Werror=maybe-uninitialized] The code is correct, but it's easy to see how the compiler gets confused here. This avoids the problem by pulling the lock outside of the function into its only caller. """ On deeper look it seems this is caused by paravirt spinlocks implementation when CONFIG_PARAVIRT_DEBUG is set, which by being complicated, manages to convince gcc locked parameter can be changed externally (impossible). Work around it by removing the conditional locking parameters altogether. (It was never the most elegant code anyway.) Slight penalty we now pay is an additional irqsave spin lock/unlock cycle on the event enable path. But since enable is not a fast path, that is preferrable to the alternative solution which was doing MMIO under irqsave spinlock. Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reported-by: Arnd Bergmann <arnd@arndb.de> Fixes: |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.