Subject: Re: [PATCH v3 36/50] functionfs: switch to simple_remove_by_name()

From: Al Viro <[email-masked]>
Date: Tue, 11 Nov 2025 09:22:44 +0000

On Tue, Nov 11, 2025 at 07:53:16AM +0000, [email-masked] wrote:

> When ffs_epfiles_create() calls ffs_epfiles_destroy(epfiles, i - 1) after
> the first ffs_sb_create_file() call fails (when i=1), it passes count=0.
> The initialization loop starts at i=1, so epfiles[0].ffs is never
> initialized.

Incorrect.  The loop in question is

	epfile = epfiles;
	for (i = 1; i <= count; ++i, ++epfile) {
		epfile->ffs = ffs;
		mutex_init(&epfile->mutex);
		mutex_init(&epfile->dmabufs_mutex);
		INIT_LIST_HEAD(&epfile->dmabufs);
		if (ffs->user_flags & FUNCTIONFS_VIRTUAL_ADDR)
			sprintf(epfile->name, "ep%02x", ffs->eps_addrmap[i]);
		else   
			sprintf(epfile->name, "ep%u", i);
		err = ffs_sb_create_file(ffs->sb, epfile->name,
					 epfile, &ffs_epfile_operations);
		if (err) {
			ffs_epfiles_destroy(epfiles, i - 1);
			return err;
		}
	}

and invariant maintained through the loop is epfile == epfiles + (i - 1).
We start with i == 1 and epfile == epfiles, modify neither variable in
the loop body and increment both i and epfile by the same amount in
the step.

In other words, on the first pass through the loop we access epfiles[0],
not epfiles[1].  Granted, the loop could've been more idiomatic, but
it is actually correct.