Messages in this thread | | | From | Jeff Moyer <> | Date | Wed, 16 Feb 2005 10:54:37 -0500 | Subject | Re: [PATCH] dcache d_drop() bug fix / __d_drop() use fix |
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==> Regarding Re: [PATCH] dcache d_drop() bug fix / __d_drop() use fix; raven@themaw.net adds:
raven> On Wed, 16 Feb 2005, Jan Blunck wrote: >> This is a re-submission of the patch I sent about a month ago. >> >> While working on my code I realized that d_drop() might race against >> __d_lookup(). __d_drop() (which is called by d_drop() after acquiring the >> dcache_lock) is accessing dentry->d_flags to set the DCACHE_UNHASHED flag. >> This shouldn't be done without holding dentry->d_lock, like stated in >> dcache.h: >> >> struct dentry { >> ... >> unsigned int d_flags; /* protected by d_lock */ >> ... >> }; >> >> Therefore d_drop() must acquire the dentry->d_lock. Likewise every use of >> __d_drop() must acquire that lock. >> >> This patch fixes d_drop() and every grep'able __d_drop() use. This patch is >> against today's http://linux.bkbits.net/linux-2.5. >>
raven> For my part, in autofs4, I would prefer:
> --- linux-2.6.9/fs/autofs4/root.c.d_lock 2005-02-16 23:15:18.000000000 +0800 > +++ linux-2.6.9/fs/autofs4/root.c 2005-02-16 23:15:35.000000000 +0800 > @@ -621,7 +621,7 @@ > spin_unlock(&dcache_lock); > return -ENOTEMPTY; > } > - __d_drop(dentry); > + d_drop(dentry); > spin_unlock(&dcache_lock);
> dput(ino->dentry);
Ian, this would deadlock. You already hold the dcache lock here, and d_drop takes it:
static inline void d_drop(struct dentry *dentry) { spin_lock(&dcache_lock); __d_drop(dentry); spin_unlock(&dcache_lock); }
The proposed patch was to take the dentry->d_lock.
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