Date: Mon, 22 Sep 2025 09:50:09 +0100 From: John Baldwin <jhb@FreeBSD.org> To: Konstantin Belousov <kib@FreeBSD.org>, src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: Re: git: 40a42785dbba - main - fcntl(F_SETFL): only allow one thread to perform F_SETFL Message-ID: <02323a46-fb47-444b-812a-1ec199a654d1@FreeBSD.org> In-Reply-To: <92831372-745d-4612-b38f-aeb235dd8cca@FreeBSD.org> References: <202509191419.58JEJsvj031867@gitrepo.freebsd.org> <92831372-745d-4612-b38f-aeb235dd8cca@FreeBSD.org>
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On 9/22/25 04:41, John Baldwin wrote: > On 9/19/25 10:19, Konstantin Belousov wrote: >> The branch main has been updated by kib: >> >> URL: https://cgit.FreeBSD.org/src/commit/?id=40a42785dbba93cc5196178fc49d340c1a89cabe >> >> commit 40a42785dbba93cc5196178fc49d340c1a89cabe >> Author: Konstantin Belousov <kib@FreeBSD.org> >> AuthorDate: 2025-09-11 10:05:04 +0000 >> Commit: Konstantin Belousov <kib@FreeBSD.org> >> CommitDate: 2025-09-19 14:19:13 +0000 >> >> fcntl(F_SETFL): only allow one thread to perform F_SETFL >> >> Use f_vflags file locking for this. >> Allowing more than one thread handling F_SETFL might cause de-sync >> between real driver state and flags. >> >> Reviewed by: markj >> Tested by: pho >> Sponsored by: The FreeBSD Foundation >> MFC after: 2 weeks >> Differential revision: https://reviews.freebsd.org/D52487 > > Thanks for fixing this. I still slightly worry that "home-grown" locks > aren't visible to WITNESS and it's checking. > > I was also expecting this to require more changes, but apparently if a > process directly invokes FIONBIO on a file descriptor, f_flags isn't > updated currently. I wonder if that is a bug. (Similarly for FIOASYNC.) > > Oh, we do handle that, but poorly. We don't revert on errors, and this > should be updated to use fsetfl_lock now I think: > > kern_ioctl(...) > { > ... > switch (com) { > ... > case FIONBIO: > if ((tmp = *(int *)data)) > atomic_set_int(&fp->f_flag, FNONBLOCK); > else > atomic_clear_int(&fp->f_flag, FNONBLOCK); > data = (void *)&tmp; > break; > case FIOASYNC: > if ((tmp = *(int *)data)) > atomic_set_int(&fp->f_flag, FASYNC); > else > atomic_clear_int(&fp->f_flag, FASYNC); > data = (void *)&tmp; > break; > } > > error = fo_ioctl(fp, com, data, td->td_ucred, td); > out: > > I think instead we want something like: > > int f_flag; > > switch (com) { > ... > case FIONBIO: > case FIOASYNC: > fsetfl_lock(fp); > tmp = *(int *)data; > f_flag = com == FIONBIO ? FNONBLOCK : FASYNC; > if ((fp->f_flag & f_flag) != 0) { This is wrong, should be: if (((fp->f_flag & f_flag) != 0) == (tmp != 0)) > fsetfl_unlock(fp); > goto out; > } > data = (void *)&tmp; > break; > } > > error = fo_ioctl(fp, com, data, td->td_ucred, td); > switch (com) { > ... > case FIONBIO: > case FIOASYNC: > if (error == 0) { > if (tmp) Probably 'if (tmp != 0)' > atomic_set_int(&fp->f_flag, f_flag); > else > atomic_clear_int(&fp->f_flag, f_flag); > } > fsetfl_unlock(fp); > break; > } > > out: > > This only updates the flag if the underlying ioctl succeeds, and it also > avoids invoking the underlying ioctl if the flag is already in the correct\ > state. > -- John Baldwin
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