Messages in this thread | | | Date | Thu, 7 May 2015 18:28:34 +0100 | From | Al Viro <> | Subject | Re: [PATCH] VFS: Add back check for !inode in walk_component() |
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On Thu, May 07, 2015 at 12:52:41PM -0400, Steven Rostedt wrote: > > Commit 698934df8b45 "VFS: Combine inode checks with d_is_negative() and > d_is_positive() in pathwalk" removed a check for inode being NULL in > walk_component() where the type is tested. Stressing my tracefs create > and remove instances while reading the files now triggers this:
So you get NULL ->d_inode with stale flags? The thing is, ->d_inode becoming NULL should happen via d_delete(), which goes throug this: unsigned flags = READ_ONCE(dentry->d_flags);
flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU); WRITE_ONCE(dentry->d_flags, flags); smp_wmb(); dentry->d_inode = NULL;
and after that assignment to ->d_flags you'll see d_is_negative() being true. OTOH, we have *inode = dentry->d_inode; if (read_seqcount_retry(&dentry->d_seq, seq)) in lookup_fast(), and read_seqcount_retry() is { smp_rmb(); return __read_seqcount_retry(s, start); }
IOW, we have smp_rmb() between fetching ->d_inode and checking ->d_flags.
If you can reproduce that at will, could you make it dump nd->flags along with dentry involved?
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