Messages in this thread |  | | Date | Sat, 11 Nov 2000 18:54:00 -0500 | Subject | Re: What protects f_pos? | From | tytso@mit ... |
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From: David Wragg <dpw@doc.ic.ac.uk> Date: 04 Nov 2000 22:16:18 +0000
Since f_pos of struct file is a loff_t, on 32-bit architectures it needs a lock to make accesses atomic (or some more sophisticated form of protection). But looking in 2.4.0-test10, there doesn't seem to be any such lock.
The llseek op is called with the Big Kernel Lock, but unlike in 2.2, the read and write ops are called without any locks held, and so generic_file_{read|write} make unprotected accesses to f_pos (through their ppos argument).
This looks like it's a bug to me.... although if you have multiple threads hitting a file descriptor at the same time, you're pretty much asking for trouble.
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