Date: Tue, 17 Jun 2003 03:44:42 -0700 (PDT) From: Don Lewis <truckman@FreeBSD.org> To: current@FreeBSD.org Subject: fdrop_locked() and FILE_LOCK() vs. Giant Message-ID: <200306171044.h5HAigM7051410@gw.catspoiler.org>
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The FILE_LOCK() implementation uses "pool mutex" under the hood, which means it should only be used as a leaf level mutex. The fdrop_locked() code wants to be called with FILE_LOCK() held, but the fdrop_locked() implementation calls mtx_lock(&Giant) before calling FILE_UNLOCK(). In addition to violating the proper usage of the "pool mutex", there is also the potential for a lock order violation. The close() implementation grabs Giant and eventually calls fdrop(), which calls FILE_LOCK() immediately before calling fdrop_locked(). If another caller of fdrop_locked() calls FILE_LOCK() without grabbing Giant first, then the lock order will be reversed when fdrop_locked() grabs Giant. It looks like fdrop_locked() should require that Giant be grabbed by the caller before fdrop_locked() is called.
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