linux-kernel - Re: [RFC 4/8] jbd, jbd2: Do not fail journal because of frozen

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Date:	Wed, 12 Aug 2015 11:14:11 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Greg Thelen <gthelen@...gle.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Dave Chinner <david@...morbit.com>,
	Theodore Ts'o <tytso@....edu>, linux-btrfs@...r.kernel.org,
	linux-ext4@...r.kernel.org, Jan Kara <jack@...e.cz>
Subject: Re: [RFC 4/8] jbd, jbd2: Do not fail journal because of
 frozen_buffer allocation failure

On Wed 05-08-15 09:49:24, Greg Thelen wrote:
> 
> mhocko@...nel.org wrote:
> 
> > From: Michal Hocko <mhocko@...e.com>
> >
> > Journal transaction might fail prematurely because the frozen_buffer
> > is allocated by GFP_NOFS request:
> > [   72.440013] do_get_write_access: OOM for frozen_buffer
> > [   72.440014] EXT4-fs: ext4_reserve_inode_write:4729: aborting transaction: Out of memory in __ext4_journal_get_write_access
> > [   72.440015] EXT4-fs error (device sda1) in ext4_reserve_inode_write:4735: Out of memory
> > (...snipped....)
> > [   72.495559] do_get_write_access: OOM for frozen_buffer
> > [   72.495560] EXT4-fs: ext4_reserve_inode_write:4729: aborting transaction: Out of memory in __ext4_journal_get_write_access
> > [   72.496839] do_get_write_access: OOM for frozen_buffer
> > [   72.496841] EXT4-fs: ext4_reserve_inode_write:4729: aborting transaction: Out of memory in __ext4_journal_get_write_access
> > [   72.505766] Aborting journal on device sda1-8.
> > [   72.505851] EXT4-fs (sda1): Remounting filesystem read-only
> >
> > This wasn't a problem until "mm: page_alloc: do not lock up GFP_NOFS
> > allocations upon OOM" because small GPF_NOFS allocations never failed.
> > This allocation seems essential for the journal and GFP_NOFS is too
> > restrictive to the memory allocator so let's use __GFP_NOFAIL here to
> > emulate the previous behavior.
> >
> > jbd code has the very same issue so let's do the same there as well.
> >
> > Signed-off-by: Michal Hocko <mhocko@...e.com>
> > ---
> >  fs/jbd/transaction.c  | 11 +----------
> >  fs/jbd2/transaction.c | 14 +++-----------
> >  2 files changed, 4 insertions(+), 21 deletions(-)
> >
> > diff --git a/fs/jbd/transaction.c b/fs/jbd/transaction.c
> > index 1695ba8334a2..bf7474deda2f 100644
> > --- a/fs/jbd/transaction.c
> > +++ b/fs/jbd/transaction.c
> > @@ -673,16 +673,7 @@ do_get_write_access(handle_t *handle, struct journal_head *jh,
> >  				jbd_unlock_bh_state(bh);
> >  				frozen_buffer =
> >  					jbd_alloc(jh2bh(jh)->b_size,
> > -							 GFP_NOFS);
> > -				if (!frozen_buffer) {
> > -					printk(KERN_ERR
> > -					       "%s: OOM for frozen_buffer\n",
> > -					       __func__);
> > -					JBUFFER_TRACE(jh, "oom!");
> > -					error = -ENOMEM;
> > -					jbd_lock_bh_state(bh);
> > -					goto done;
> > -				}
> > +							 GFP_NOFS|__GFP_NOFAIL);
> >  				goto repeat;
> >  			}
> >  			jh->b_frozen_data = frozen_buffer;
> > diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> > index ff2f2e6ad311..bff071e21553 100644
> > --- a/fs/jbd2/transaction.c
> > +++ b/fs/jbd2/transaction.c
> > @@ -923,16 +923,7 @@ do_get_write_access(handle_t *handle, struct journal_head *jh,
> >  				jbd_unlock_bh_state(bh);
> >  				frozen_buffer =
> >  					jbd2_alloc(jh2bh(jh)->b_size,
> > -							 GFP_NOFS);
> > -				if (!frozen_buffer) {
> > -					printk(KERN_ERR
> > -					       "%s: OOM for frozen_buffer\n",
> > -					       __func__);
> > -					JBUFFER_TRACE(jh, "oom!");
> > -					error = -ENOMEM;
> > -					jbd_lock_bh_state(bh);
> > -					goto done;
> > -				}
> > +							 GFP_NOFS|__GFP_NOFAIL);
> >  				goto repeat;
> >  			}
> >  			jh->b_frozen_data = frozen_buffer;
> > @@ -1157,7 +1148,8 @@ int jbd2_journal_get_undo_access(handle_t *handle, struct buffer_head *bh)
> >  
> >  repeat:
> >  	if (!jh->b_committed_data) {
> > -		committed_data = jbd2_alloc(jh2bh(jh)->b_size, GFP_NOFS);
> > +		committed_data = jbd2_alloc(jh2bh(jh)->b_size,
> > +					    GFP_NOFS|__GFP_NOFAIL);
> >  		if (!committed_data) {
> >  			printk(KERN_ERR "%s: No memory for committed data\n",
> >  				__func__);
> 
> Is this "if (!committed_data) {" check now dead code?
> 
> I also see other similar suspected dead sites in the rest of the series.

You are absolutely right. I have updated the patches.

Thanks!
-- 
Michal Hocko
SUSE Labs
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