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lock is obtained before the write count is increased during open() and the lock is released after the write count is decreased during close(). The first change closes a race where an open() that will block with O_SHLOCK or O_EXLOCK can increase the write count while it waits. If the process holding the current lock on the file then tries to call exec() on the file it has locked, it can fail with ETXTBUSY even though the advisory lock is preventing other threads from succesfully completeing a writable open(). The second change closes a race where a read-only open() with O_SHLOCK or O_EXLOCK may return successfully while the write count is non-zero due to another descriptor that had the advisory lock and was blocking the open() still being in the process of closing. If the process that completed the open() then attempts to call exec() on the file it locked, it can fail with ETXTBUSY even though the other process that held a write lock has closed the file and released the lock. Reviewed by: kib MFC after: 1 month
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