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Alexey Dobriyan
b2f5de0334
* Test lookup in /proc/self/fd. "map_files" lookup story showed that lookup is not that simple. * Test that all those symlinks open the same file. Check with (st_dev, st_info). * Test that kernel threads do not have anything in their /proc/*/fd/ directory. Now this is where things get interesting. First, kernel threads aren't pinned by /proc/self or equivalent, thus some "atomicity" is required. Second, ->comm can contain whitespace and ')'. No, they are not escaped. Third, the only reliable way to check if process is kernel thread appears to be field #9 in /proc/*/stat. This field is struct task_struct::flags in decimal! Check is done by testing PF_KTHREAD flags like we do in kernel. PF_KTREAD value is a part of userspace ABI !!! Other methods for determining kernel threadness are not reliable: * RSS can be 0 if everything is swapped, even while reading from /proc/self. * ->total_vm CAN BE ZERO if process is finishing munmap(NULL, whole address space); * /proc/*/maps and similar files can be empty because unmapping everything works. Read returning 0 can't distinguish between kernel thread and such suicide process. Link: http://lkml.kernel.org/r/20180505000414.GA15090@avx2 Signed-off-by: Alexey Dobriyan <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>