From: Michal Hocko <mhocko@kernel.org> To: Omar Sandoval <osandov@osandov.com> Cc: kernel test robot <xiaolong.ye@intel.com>, Vinnie Magro <vmagro@fb.com>, David Sterba <dsterba@suse.com>, Omar Sandoval <osandov@fb.com>, LKML <linux-kernel@vger.kernel.org>, Stephen Rothwell <sfr@canb.auug.org.au>, lkp@01.org Subject: Re: [lkp-robot] [btrfs] beeeccca9b: WARNING:at_mm/util.c:#kvmalloc_node Date: Wed, 31 May 2017 11:19:05 +0200 [thread overview] Message-ID: <20170531091904.GD27783@dhcp22.suse.cz> (raw) In-Reply-To: <20170531091202.GA769@vader> 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. -- Michal Hocko SUSE Labs
WARNING: multiple messages have this Message-ID (diff)
From: Michal Hocko <mhocko@kernel.org> To: lkp@lists.01.org Subject: Re: [lkp-robot] [btrfs] beeeccca9b: WARNING:at_mm/util.c:#kvmalloc_node Date: Wed, 31 May 2017 11:19:05 +0200 [thread overview] Message-ID: <20170531091904.GD27783@dhcp22.suse.cz> (raw) In-Reply-To: <20170531091202.GA769@vader> [-- Attachment #1: Type: text/plain, Size: 1679 bytes --] 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. -- Michal Hocko SUSE Labs
next prev parent reply other threads:[~2017-05-31 9:19 UTC|newest] Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-05-31 6:30 [lkp-robot] [btrfs] beeeccca9b: WARNING:at_mm/util.c:#kvmalloc_node kernel test robot 2017-05-31 6:30 ` kernel test robot 2017-05-31 6:51 ` Michal Hocko 2017-05-31 6:51 ` Michal Hocko 2017-05-31 9:12 ` Omar Sandoval 2017-05-31 9:12 ` Omar Sandoval 2017-05-31 9:19 ` Michal Hocko [this message] 2017-05-31 9:19 ` Michal Hocko 2017-05-31 9:29 ` Omar Sandoval 2017-05-31 9:29 ` Omar Sandoval 2017-05-31 10:30 ` Michal Hocko 2017-05-31 10:30 ` Michal Hocko 2017-05-31 14:58 ` David Sterba 2017-05-31 14:58 ` David Sterba 2017-06-05 3:30 ` Stephen Rothwell 2017-06-05 3:30 ` Stephen Rothwell 2017-06-05 11:43 ` David Sterba 2017-06-05 11:43 ` David Sterba 2017-06-05 12:11 ` Stephen Rothwell 2017-06-05 12:11 ` Stephen Rothwell
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