Messages in this thread | | | Date | Fri, 1 Feb 2013 19:34:02 +0000 | From | Al Viro <> | Subject | Re: [PATCH] Tracepoint: Add 'file name' as a parameter of tracepoint events ext4:ext4_direct_IO_enter&ext4:ext4_direct_IO_exit |
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On Fri, Feb 01, 2013 at 11:37:38PM +0800, chenggang.qin@gmail.com wrote: > @@ -3213,13 +3214,15 @@ static ssize_t ext4_direct_IO(int rw, struct kiocb *iocb, > if (ext4_has_inline_data(inode)) > return 0; > > - trace_ext4_direct_IO_enter(inode, offset, iov_length(iov, nr_segs), rw); > + fname = file->f_path.dentry->d_name.name; > + trace_ext4_direct_IO_enter(inode, offset, iov_length(iov, nr_segs), rw, > + fname);
Oh, wonderful... "your patch is racy; there's no warranty that fname will not be freed right under you" -- "OK, we shouldn't do it in VFS... let's try to do exact same thing in ext4, then"
Let me spell it out for you: opened files *can* be renamed while they are in the middle of IO. If both old and new names are short, the contents of ->d_name.name will be overwritten, so dereferencing your fname can yield a mix of old and new name, or something that isn't NUL-terminated. If they are long enough, they will be allocated separately from struct dentry and your fname can bloody well end up pointing to freed memory by the time you get around to dereferencing it.
Again, there is no exclusion between ext4_direct_IO() (or its callers) and rename(). The NAK still stands.
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