Date: Wed, 02 Aug 2006 23:52:29 -0500 From: Eric Anderson <anderson@centtech.com> To: Eric Anderson <anderson@centtech.com> Cc: freebsd-fs@freebsd.org Subject: Re: locking questions (regarding file systems) Message-ID: <44D1810D.9070808@centtech.com> In-Reply-To: <44D176AF.8020300@centtech.com> References: <20060802193408.47760.qmail@web30301.mail.mud.yahoo.com> <44D176AF.8020300@centtech.com>
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On 08/02/06 23:08, Eric Anderson wrote: > On 08/02/06 14:34, R. B. Riddick wrote: >> --- Eric Anderson <anderson@centtech.com> wrote: >>> Here's basically what I do: >>> in the mount function for the FS, I do something like this: >>> >>> DROP_GIANT(); >>> g_topology_lock(); >>> error = g_vfs_open(devvp, &cp, "fsname", 0); >>> g_topology_unlock(); >>> PICKUP_GIANT(); >>> >>> What is needed in my unmount function to release those locks? I've >>> tried some combinations of things, like: >>> >>> DROP_GIANT(); >>> g_topology_lock(); >>> # wedges here >>> g_vfs_close(cp, td); >>> g_topology_unlock(); >>> PICKUP_GIANT(); >>> vrele(devvp); >>> >> So the first un-mount works fine? >> And the second un-mount wedges _before_ g_vfs_close? >> >> I cannot find anything really suspicious in ur code... >> >> Just 2 thoughts: >> >> 1. Do we really hold GIANT, when we mount and un-mount something? >> >> 2. R u sure, that we need vrele()? I mean: Why doesn't g_vfs_close() call >> vrele(), if g_vfs_open() increases that use-count variable? Can u print the >> use-count variable in the beginning and the end of the mount/un-mount > > Looks like after mounting it, the use_count is 1. When unmounting, it > starts at 1, and moves to 0 after doing a vflush, a g_topology_lock, but > before the g_vfs_close. > > Here's the unmount code snippet: > > # here use_count is 1 > error = vflush(mp, 1, flags, td); > if (error) > return (error); > > DROP_GIANT(); > g_topology_lock(); > # this is where the use_count is now zero, and it blocks > g_vfs_close(cp, td); > g_topology_unlock(); > PICKUP_GIANT(); > vrele(devvp); > > Is it blocking because the use_count is already 0? Is the vflush > breaking things? Actually, I misinformed you earlier - I can't actually unmount, because it hangs during the first unmount. It will only unmount successfully if I remove the block above (the DROP_GIANT down to PICKUP_GIANT). Eric -- ------------------------------------------------------------------------ Eric Anderson Sr. Systems Administrator Centaur Technology Anything that works is better than anything that doesn't. ------------------------------------------------------------------------
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