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Brian Behlendorf
eb0f407a2b
PF_NOFS is a per-process debug flag which is set in current->flags to detect when a process is performing an unsafe allocation. All tasks with PF_NOFS set must strictly use KM_PUSHPAGE for allocations because if they enter direct reclaim and initiate I/O they may deadlock. When debugging is disabled, any incorrect usage will be detected and a call stack with a warning will be printed to the console. The flags will then be automatically corrected to allow for safe execution. If debugging is enabled this will be treated as a fatal condition. To avoid any risk of conflicting with the existing PF_ flags. The PF_NOFS bit shadows the rarely used PF_MUTEX_TESTER bit. Only when CONFIG_RT_MUTEX_TESTER is not set, and we know this bit is unused, will the PF_NOFS bit be valid. Happily, most existing distributions ship a kernel with CONFIG_RT_MUTEX_TESTER disabled. Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>