From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <46B87F93.9020308@domain.hid> Date: Tue, 07 Aug 2007 16:20:03 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <46B86E53.1030803@domain.hid> <46B86FE4.3040209@domain.hid> <46B87B85.1080304@domain.hid> <2ff1a98a0708070711n5e97ca03y18aef78ececc7e0d@domain.hid> In-Reply-To: <2ff1a98a0708070711n5e97ca03y18aef78ececc7e0d@domain.hid> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigB656B1DAE2B13DA18A04A588" Sender: jan.kiszka@domain.hid Subject: Re: [Xenomai-core] [Adeos-main] [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) --------------enigB656B1DAE2B13DA18A04A588 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: quoted-printable Gilles Chanteperdrix wrote: > On 8/7/07, Jan Kiszka wrote: >> 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 i= s >>>> broken. But the good new is that this might be easily fixable by >>>> providing the right gfp_mask. GFP_ATOMIC? >>> 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 ha= ve >> 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 t= he >> loop in copy_pte_range. But that may require more code changes. >=20 > I would say the real fix is to drop momentarily the spinlock(s?) for al= locating. >=20 Are you sure it's safe to drop locks in the (logical) middle of copy_one_pte()? I can't tell yet from the few glances I took. It's just my feeling that says "no" so far. Jan --------------enigB656B1DAE2B13DA18A04A588 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 iD8DBQFGuH+TniDOoMHTA+kRApx9AJ9PboWZfo1argaKghcz0TqvT21kPgCghUAt m2fz80B7skfTMkVAWWPqCGk= =CsJe -----END PGP SIGNATURE----- --------------enigB656B1DAE2B13DA18A04A588--