From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <46B87B85.1080304@domain.hid> Date: Tue, 07 Aug 2007 16:02:45 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <46B86E53.1030803@domain.hid> <46B86FE4.3040209@domain.hid> In-Reply-To: <46B86FE4.3040209@domain.hid> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig3219BBC2193E0210043EF981" Sender: jan.kiszka@domain.hid Subject: Re: [Xenomai-core] [COW-BUG] __alloc_pages called from atomic context List-Id: "Xenomai life and development \(bug reports, patches, discussions\)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix Cc: adeos-main , xenomai-core This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig3219BBC2193E0210043EF981 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: quoted-printable Gilles Chanteperdrix wrote: > Jan Kiszka wrote: >> Hi all, >> >> we are getting a lot of >> >> BUG: sleeping function called from invalid context at mm/page_alloc.c:= 1225 >> in_atomic():1, irqs_disabled():0 >> [] show_trace_log_lvl+0x1a/0x2f >> [] show_trace+0x12/0x14 >> [] dump_stack+0x16/0x18 >> [] __might_sleep+0xcd/0xd3 >> [] __alloc_pages+0x32/0x281 >> [] copy_page_range+0x221/0x41e >> [] copy_process+0x9e1/0xfe2 >> [] do_fork+0x99/0x176 >> [] sys_clone+0x33/0x39 >> [] syscall_call+0x7/0xb >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= >> >> here due to a Xenomai program issuing system() calls. >> >> After once again dissecting the "nice" mm code (sigh...), the reason >> turned out to be plain simple: >> >> copy_pte_range(...); >> spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING); >> copy_one_pte(...); >> if (is_cow_mapping(vm_flags)) >> alloc_page_vma(GFP_HIGHUSER, ...); >> __alloc_pages(...) >> might_sleep_if(gfp_mask & __GFP_WAIT); >> >> And this is true due to #define GFP_HIGHUSER (__GFP_WAIT | ... >> >> So the bad news is that the COW code in likely all i-pipe versions is >> broken. But the good new is that this might be easily fixable by >> providing the right gfp_mask. GFP_ATOMIC? >=20 > It does not look like a good solution, you are going to empty the > GFP_ATOMIC pools. The proper solution would rather be to look at the > real mm code (I mean not the one I wrote) and see how they cope with > this issue. Mmpf. What are the chances for a quick fix within the next days? We have to consider alternatives right now here because the whole system is meant for production purpose next week (C-ELROB '07). OK, I'm already finding myself inside the code :-/. What about this approach: We try to alloc with GFP_ATOMIC. Once this fails, we break out, drop all locks (just like it happens in case of need_resched()), try to fill up the pool, and restart then. What would reliably make Linux refill its atomic pool? Alternative approach: preallocate the required pages before entering the loop in copy_pte_range. But that may require more code changes. Jan --------------enig3219BBC2193E0210043EF981 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFGuHuFniDOoMHTA+kRAnDMAJ9xIEeZAcMyLUQh2+mpIQ4d50IaAgCeJm4Q 0p2ARTASmjSN8K1p1Fr1yF4= =h8kE -----END PGP SIGNATURE----- --------------enig3219BBC2193E0210043EF981--