Messages in this thread | | | Date | Wed, 10 Jan 2024 17:31:49 -0500 | From | Rafael Aquini <> | Subject | Re: [PATCH v2] workqueue.c: Increase workqueue name length |
| |
On Wed, Jan 10, 2024 at 11:06:22PM +0100, Rasmus Villemoes wrote: > On 10/01/2024 22.52, Rafael Aquini wrote: > > On Wed, Jan 10, 2024 at 09:47:56PM +0100, Rasmus Villemoes wrote: > >> On 10/01/2024 21.29, Audra Mitchell wrote: > >> > >>> @@ -4663,9 +4663,10 @@ struct workqueue_struct *alloc_workqueue(const char *fmt, > >>> unsigned int flags, > >>> int max_active, ...) > >>> { > >>> - va_list args; > >>> + va_list args, args_copy; > >>> struct workqueue_struct *wq; > >>> struct pool_workqueue *pwq; > >>> + int len; > >>> > >>> /* > >>> * Unbound && max_active == 1 used to imply ordered, which is no longer > >>> @@ -4692,6 +4693,13 @@ struct workqueue_struct *alloc_workqueue(const char *fmt, > >>> } > >>> > >>> va_start(args, max_active); > >>> + va_copy(args_copy, args); > >>> + len = vsnprintf(NULL, 0, fmt, args_copy); > >>> + WARN(len > WQ_NAME_LEN, > >>> + "workqueue: wq->name too long (%d). Truncated to WQ_NAME_LEN (%d)\n", > >>> + len, WQ_NAME_LEN); > >>> + > >>> + va_end(args_copy); > >>> vsnprintf(wq->name, sizeof(wq->name), fmt, args); > >> > >> Eh, why not just _not_ throw away the return value from the existing > >> vsnprintf() and do "len >= sizeof(wq->name)" to know if truncation > >> happened? There's really no need need to do vsnprintf() twice. (And yes, > >> you want >=, not >). > >> > > > > The extra vsnprintf call is required because the return of the existing > > vsnprintf() is going to be already capped by sizeof(wq->name). > > No, it is not. vsnprintf() returns the length of the would-be-created > string if the buffer was big enough. That is independent of whether one > does a dummy NULL,0 call or just calls it with a real, but possibly too > small, buffer. > > This is true for userspace (as required by posix) as well as the kernel > implementation of vsnprintf(). What makes you think otherwise? >
this snippet from PRINTF(3) man page
RETURN VALUE Upon successful return, these functions return the number of characters printed (excluding the null byte used to end output to strings).
> The kernel _also_ happens to have a non-standardized function called > vscnprintf (note the c) which returns the possibly-truncated result. But > that's irrelevant here. > > >> Oh, and definitely not WARN, pr_warn() or pr_warn_once() please. > >> > > > > Then you lose the ability to figure out what was trying to create the > > wq with the inflated name. Also, the _once variants don't seem to do > > good here, because alloc_workqueue() can be called by different > > drivers. > > I assume that whatever creates the wq will do so on every boot, and the > name is most likely some fixed thing. So you're essentially setting up > some configurations to do a WARN on every single boot, not to mention > that for some machines that implies a panic... It really is not > something that warrants a WARN. > > As for figuring out what caused that too-long name, well, I'd hope that > the 31 meaningful bytes that did get produced would provide a > sufficiently good hint. > > Rasmus >
| |