From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751297AbdEaKam (ORCPT ); Wed, 31 May 2017 06:30:42 -0400 Received: from mx2.suse.de ([195.135.220.15]:44390 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750992AbdEaKak (ORCPT ); Wed, 31 May 2017 06:30:40 -0400 Date: Wed, 31 May 2017 12:30:32 +0200 From: Michal Hocko To: Omar Sandoval Cc: kernel test robot , Vinnie Magro , David Sterba , Omar Sandoval , LKML , Stephen Rothwell , lkp@01.org Subject: Re: [lkp-robot] [btrfs] beeeccca9b: WARNING:at_mm/util.c:#kvmalloc_node Message-ID: <20170531103031.GG27783@dhcp22.suse.cz> References: <20170531063033.GC1795@yexl-desktop> <20170531065128.GB3853@dhcp22.suse.cz> <20170531091202.GA769@vader> <20170531091904.GD27783@dhcp22.suse.cz> <20170531092920.GA1418@vader> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170531092920.GA1418@vader> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 31-05-17 02:29:20, Omar Sandoval wrote: > On Wed, May 31, 2017 at 11:19:05AM +0200, Michal Hocko wrote: > > On Wed 31-05-17 02:12:02, Omar Sandoval wrote: > > > On Wed, May 31, 2017 at 08:51:28AM +0200, Michal Hocko wrote: > > > > On Wed 31-05-17 14:30:33, kernel test robot wrote: > > > > > > > > > > FYI, we noticed the following commit: > > > > > > > > > > commit: beeeccca9bebcec386cc31c250cff8a06cf27034 ("btrfs: Use kvzalloc instead of kzalloc/vmalloc in alloc_bitmap") > > > > > https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master > > > > > > > > I have intentionally skipped alloc_bitmap because it relies on GFP_NOFS. > > > > This doesn't work properly when falling back to vmalloc and that is what > > > > the warning reported here says. I believe the right approach is to check > > > > whether the GFP_NOFS is _really_ needed and document why if yes. > > > > Otherwise drop the NOFS part in one patch with the explanation and > > > > convert it to kvmalloc in a separate patch. > > > > > > Unfortunately we really do need GFP_NOFS here, the free space tree is > > > modified while we are committing a fs transaction, sometimes in the > > > critical section when we block new operations from joining the > > > transaction. > > > > OK, please document this. > > > > > Looking at the comment in kvmalloc_node(): > > > > > > /* > > > * vmalloc uses GFP_KERNEL for some internal allocations (e.g page tables) > > > * so the given set of flags has to be compatible. > > > */ > > > WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL); > > > > > > has alloc_bitmap() always been broken by virtue of calling vmalloc() > > > with GFP_NOFS? > > > > yes. vmalloc is simply not GFP_NOFS safe as it performs GFP_KERNEL > > hardcoded allocations. The way out of this is to use > > memalloc_nofs_{save,restore} around kvmalloc call. > > Ok, thanks. Something like this untested patch instead of the one in > linux-next? > > diff --git a/fs/btrfs/free-space-tree.c b/fs/btrfs/free-space-tree.c > index fc0bd8406758..5abd3cd71144 100644 > --- a/fs/btrfs/free-space-tree.c > +++ b/fs/btrfs/free-space-tree.c > @@ -153,21 +153,18 @@ static inline u32 free_space_bitmap_size(u64 size, u32 sectorsize) > > static u8 *alloc_bitmap(u32 bitmap_size) > { > - void *mem; > + u8 *ret; > + unsigned int nofs_flag; > > /* > - * The allocation size varies, observed numbers were < 4K up to 16K. > - * Using vmalloc unconditionally would be too heavy, we'll try > - * contiguous allocations first. > + * GFP_NOFS doesn't work with kvmalloc(), but we really can't recurse > + * into the filesystem as the free space bitmap can be modified in the > + * critical section of a transaction commit. > */ I would just place * TODO - make sure memalloc_nofs_{save,restore} is called at * caller of this function - ideally when the transaction * starts/stops. */ > - if (bitmap_size <= PAGE_SIZE) > - return kzalloc(bitmap_size, GFP_NOFS); > - > - mem = kzalloc(bitmap_size, GFP_NOFS | __GFP_NOWARN); > - if (mem) > - return mem; > - > - return __vmalloc(bitmap_size, GFP_NOFS | __GFP_ZERO, PAGE_KERNEL); > + nofs_flag = memalloc_nofs_save(); > + ret = kvmalloc(bitmap_size, GFP_KERNEL); > + memalloc_nofs_restore(nofs_flag); > + return ret; > } > > int convert_free_space_to_bitmaps(struct btrfs_trans_handle *trans, > > Dave, would you prefer to replace the patch we have now or do an > incremental patch on top of it? > > Michal, is there some reason we can't have kvmalloc() with > !(gfp & __GFP_FS) just do the memalloc_nofs dance internally? Yes, we really want to mark the transaction or other recursion dangerous contexts at the places where the context starts/stops. kvmalloc is definitely not the proper place to play those tricks. -- Michal Hocko SUSE Labs From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: multipart/mixed; boundary="===============7747628812716893392==" MIME-Version: 1.0 From: Michal Hocko To: lkp@lists.01.org Subject: Re: [lkp-robot] [btrfs] beeeccca9b: WARNING:at_mm/util.c:#kvmalloc_node Date: Wed, 31 May 2017 12:30:32 +0200 Message-ID: <20170531103031.GG27783@dhcp22.suse.cz> In-Reply-To: <20170531092920.GA1418@vader> List-Id: --===============7747628812716893392== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable On Wed 31-05-17 02:29:20, Omar Sandoval wrote: > On Wed, May 31, 2017 at 11:19:05AM +0200, Michal Hocko wrote: > > On Wed 31-05-17 02:12:02, Omar Sandoval wrote: > > > On Wed, May 31, 2017 at 08:51:28AM +0200, Michal Hocko wrote: > > > > On Wed 31-05-17 14:30:33, kernel test robot wrote: > > > > > = > > > > > FYI, we noticed the following commit: > > > > > = > > > > > commit: beeeccca9bebcec386cc31c250cff8a06cf27034 ("btrfs: Use kvz= alloc instead of kzalloc/vmalloc in alloc_bitmap") > > > > > https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git = master > > > > = > > > > I have intentionally skipped alloc_bitmap because it relies on GFP_= NOFS. > > > > This doesn't work properly when falling back to vmalloc and that is= what > > > > the warning reported here says. I believe the right approach is to = check > > > > whether the GFP_NOFS is _really_ needed and document why if yes. > > > > Otherwise drop the NOFS part in one patch with the explanation and > > > > convert it to kvmalloc in a separate patch. > > > = > > > Unfortunately we really do need GFP_NOFS here, the free space tree is > > > modified while we are committing a fs transaction, sometimes in the > > > critical section when we block new operations from joining the > > > transaction. > > = > > OK, please document this. > > = > > > Looking at the comment in kvmalloc_node(): > > > = > > > /* > > > * vmalloc uses GFP_KERNEL for some internal allocations (e.g page t= ables) > > > * so the given set of flags has to be compatible. > > > */ > > > WARN_ON_ONCE((flags & GFP_KERNEL) !=3D GFP_KERNEL); > > > = > > > has alloc_bitmap() always been broken by virtue of calling vmalloc() > > > with GFP_NOFS? > > = > > yes. vmalloc is simply not GFP_NOFS safe as it performs GFP_KERNEL > > hardcoded allocations. The way out of this is to use > > memalloc_nofs_{save,restore} around kvmalloc call. > = > Ok, thanks. Something like this untested patch instead of the one in > linux-next? > = > diff --git a/fs/btrfs/free-space-tree.c b/fs/btrfs/free-space-tree.c > index fc0bd8406758..5abd3cd71144 100644 > --- a/fs/btrfs/free-space-tree.c > +++ b/fs/btrfs/free-space-tree.c > @@ -153,21 +153,18 @@ static inline u32 free_space_bitmap_size(u64 size, = u32 sectorsize) > = > static u8 *alloc_bitmap(u32 bitmap_size) > { > - void *mem; > + u8 *ret; > + unsigned int nofs_flag; > = > /* > - * The allocation size varies, observed numbers were < 4K up to 16K. > - * Using vmalloc unconditionally would be too heavy, we'll try > - * contiguous allocations first. > + * GFP_NOFS doesn't work with kvmalloc(), but we really can't recurse > + * into the filesystem as the free space bitmap can be modified in the > + * critical section of a transaction commit. > */ I would just place * TODO - make sure memalloc_nofs_{save,restore} is called at * caller of this function - ideally when the transaction * starts/stops. */ > - if (bitmap_size <=3D PAGE_SIZE) > - return kzalloc(bitmap_size, GFP_NOFS); > - > - mem =3D kzalloc(bitmap_size, GFP_NOFS | __GFP_NOWARN); > - if (mem) > - return mem; > - > - return __vmalloc(bitmap_size, GFP_NOFS | __GFP_ZERO, PAGE_KERNEL); > + nofs_flag =3D memalloc_nofs_save(); > + ret =3D kvmalloc(bitmap_size, GFP_KERNEL); > + memalloc_nofs_restore(nofs_flag); > + return ret; > } > = > int convert_free_space_to_bitmaps(struct btrfs_trans_handle *trans, > = > Dave, would you prefer to replace the patch we have now or do an > incremental patch on top of it? > = > Michal, is there some reason we can't have kvmalloc() with > !(gfp & __GFP_FS) just do the memalloc_nofs dance internally? Yes, we really want to mark the transaction or other recursion dangerous contexts at the places where the context starts/stops. kvmalloc is definitely not the proper place to play those tricks. -- = Michal Hocko SUSE Labs --===============7747628812716893392==--