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

[Christian Brauner <brauner@kernel.org>]

On Tue, Nov 11, 2025 at 09:22:44AM +0000, Al Viro wrote:
> On Tue, Nov 11, 2025 at 07:53:16AM +0000, bot+bpf-ci@kernel.org 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

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> 
> 	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.