Date: Thu, 6 Mar 2025 12:35:34 +0100 From: Mateusz Guzik <mjguzik@gmail.com> To: Zhenlei Huang <zlei@freebsd.org> Cc: Mateusz Guzik <mjg@freebsd.org>, "src-committers@freebsd.org" <src-committers@freebsd.org>, "dev-commits-src-all@freebsd.org" <dev-commits-src-all@freebsd.org>, Warner Losh <imp@freebsd.org>, "dev-commits-src-main@freebsd.org" <dev-commits-src-main@freebsd.org> Subject: Re: git: 234683726708 - main - devclass: make devclass_alloc_unit use M_NOWAIT Message-ID: <CAGudoHF=eRaHCcjRrvd4sG4-OBu0GrmVRpiHEeU1ayG=M9oXrg@mail.gmail.com> In-Reply-To: <F1B3652E-0D0C-402A-8509-D510992DAC15@FreeBSD.org> References: <202503061103.526B32Id022652@gitrepo.freebsd.org> <F1B3652E-0D0C-402A-8509-D510992DAC15@FreeBSD.org>
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On Thu, Mar 6, 2025 at 12:32=E2=80=AFPM Zhenlei Huang <zlei@freebsd.org> wr= ote: > > > > On Mar 6, 2025, at 7:03 PM, Mateusz Guzik <mjg@FreeBSD.org> wrote: > > The branch main has been updated by mjg: > > URL: https://cgit.FreeBSD.org/src/commit/?id=3D234683726708cf5212d672d676= d30056d4133859 > > commit 234683726708cf5212d672d676d30056d4133859 > Author: Mateusz Guzik <mjg@FreeBSD.org> > AuthorDate: 2025-03-06 11:01:49 +0000 > Commit: Mateusz Guzik <mjg@FreeBSD.org> > CommitDate: 2025-03-06 11:01:49 +0000 > > devclass: make devclass_alloc_unit use M_NOWAIT > > The only caller already does this. > > The routine can be called with a mutex held making M_WAITOK illegal. > > Sponsored by: Rubicon Communications, LLC ("Netgate") > --- > sys/kern/subr_bus.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/sys/kern/subr_bus.c b/sys/kern/subr_bus.c > index 9506e471705c..0422352bba51 100644 > --- a/sys/kern/subr_bus.c > +++ b/sys/kern/subr_bus.c > @@ -1208,6 +1208,7 @@ devclass_get_sysctl_tree(devclass_t dc) > static int > devclass_alloc_unit(devclass_t dc, device_t dev, int *unitp) > { > + device_t *devices; > const char *s; > int unit =3D *unitp; > > @@ -1264,8 +1265,11 @@ devclass_alloc_unit(devclass_t dc, device_t dev, i= nt *unitp) > int newsize; > > newsize =3D unit + 1; > - dc->devices =3D reallocf(dc->devices, > - newsize * sizeof(*dc->devices), M_BUS, M_WAITOK); > + devices =3D reallocf(dc->devices, > + newsize * sizeof(*dc->devices), M_BUS, M_NOWAIT); > > > I'd recommend against this. From the commit message of f3d3c63442ff, Warn= er said, > > In addition, transition to M_WAITOK since this is a sleepable context > So, the M_WAITOK is intentional. > > Rather than reverting this, the caller devclass_add_device() should use M= _WAITOK. > Per my commit message this is callable from a *NOT* sleepable context. Here is a splat we got at Netgate: uma_zalloc_debug: zone "malloc-16" with the following non-sleepable locks h= eld: exclusive sleep mutex SD slot mtx (sdhci) r =3D 0 (0xd8dec028) locked @ /var/jenkins/workspace/pfSense-Plus-snapshots-25_03-main/sources/FreeBSD-sr= c-plus-RELENG_25_03/sys/dev/sdhci/sdhci.c:688 stack backtrace: #0 0xc0330ebc at witness_debugger+0x78 #1 0xc033217c at witness_warn+0x428 #2 0xc05b0a58 at uma_zalloc_debug+0x34 #3 0xc05b067c at uma_zalloc_arg+0x30 #4 0xc0291760 at malloc+0x8c #5 0xc02920ec at reallocf+0x14 #6 0xc02f8894 at devclass_add_device+0x1e8 #7 0xc02f6c78 at make_device+0xe0 #8 0xc02f6abc at device_add_child_ordered+0x30 #9 0xc0156e0c at sdhci_card_task+0x238 #10 0xc0324090 at taskqueue_run_locked+0x1b4 #11 0xc0323ea0 at taskqueue_run+0x50 #12 0xc0275f88 at ithread_loop+0x264 #13 0xc0271f28 at fork_exit+0xa0 #14 0xc05f82d4 at swi_exit+0 It may be some callers are sleepable. Perhaps a different variant accepting flags would be prudent, but I have no interest in looking into that. > ``` > - dev->nameunit =3D malloc(buflen, M_BUS, M_NOWAIT|M_ZERO); > - if (!dev->nameunit) > - return (ENOMEM); > + dev->nameunit =3D malloc(buflen, M_BUS, M_WAITOK | M_ZERO); > ``` > > Best regards, > Zhenlei > > + if (devices =3D=3D NULL) > + return (ENOMEM); > + dc->devices =3D devices; > memset(dc->devices + dc->maxunit, 0, > sizeof(device_t) * (newsize - dc->maxunit)); > dc->maxunit =3D newsize; > > > > --=20 Mateusz Guzik <mjguzik gmail.com>
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