linux-kernel - Re: [PATCH V1] f2fs: fix potentail deadloop issue in do_recover

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Date: Mon, 22 Jan 2024 13:46:58 +0800
From: Zhiguo Niu <niuzhiguo84@...il.com>
To: Chao Yu <chao@...nel.org>
Cc: Zhiguo Niu <zhiguo.niu@...soc.com>, jaegeuk@...nel.org, 
	linux-f2fs-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org, 
	ke.wang@...soc.com
Subject: Re: [PATCH V1] f2fs: fix potentail deadloop issue in do_recover_data

Hi Chao

On Mon, Jan 22, 2024 at 11:46 AM Chao Yu <chao@...nel.org> wrote:
>
> On 2023/12/25 19:11, Zhiguo Niu wrote:
> > There is a potentail deadloop issue in the corner case of
> > CONFIG_F2FS_FAULT_INJECTION is enabled and the return value
> > of f2fs_reserve_new_block is error but not -ENOSPC, such as
> > this error case:
> > if (unlikely(is_inode_flag_set(dn->inode, FI_NO_ALLOC)))
> >               return -EPERM;
>
> I don't see any path to trigger this error? am I missing something?
>
> > besides, the mainly error -ENOSPC has been handled as bug on,
> > so other error cases can be proecssed normally without looping.
>
> commit 975756c41332bc5e523e9f843271ed5ab6aaaaaa
> Author: Jaegeuk Kim <jaegeuk@...nel.org>
> Date:   Thu May 19 11:57:21 2016 -0700
>
>      f2fs: avoid ENOSPC fault in the recovery process
>
>      This patch avoids impossible error injection, ENOSPC, during recovery process.
>
> Please check above patch, I guess intention of adding such loop is
> to avoid mount failure due to fault injection was triggered in
> f2fs_reserve_new_block().
>
> What about change as blew?
> - keep the loop to avoid mount failure.
> - remove bug_on() to avoid panic due to fault injection error.
>
> #define DEFAULT_RETRY_COUNT             8
>
>                 for (loops = DEFAULT_RETRY_COUNT; loops > 0; loops--) {
>                         err = f2fs_reserve_new_block(&dn);
>                         if (!err ||
>                                 !IS_ENABLED(CONFIG_F2FS_FAULT_INJECTION))
>                                 break;
>                 }

Thanks for your detailed explanation and I understand.
It seems that the original process is also reasonable,
so it’s okay to keep it as it is.
>
> Thanks,
>
> >
> > Fixes: 956fa1ddc132 ("f2fs: fix to check return value of f2fs_reserve_new_block()")
> > Signed-off-by: Zhiguo Niu <zhiguo.niu@...soc.com>
> > ---
> >   fs/f2fs/recovery.c | 26 ++++++++------------------
> >   1 file changed, 8 insertions(+), 18 deletions(-)
> >
> > diff --git a/fs/f2fs/recovery.c b/fs/f2fs/recovery.c
> > index 21381b7..5d658f6 100644
> > --- a/fs/f2fs/recovery.c
> > +++ b/fs/f2fs/recovery.c
> > @@ -710,15 +710,10 @@ static int do_recover_data(struct f2fs_sb_info *sbi, struct inode *inode,
> >                */
> >               if (dest == NEW_ADDR) {
> >                       f2fs_truncate_data_blocks_range(&dn, 1);
> > -                     do {
> > -                             err = f2fs_reserve_new_block(&dn);
> > -                             if (err == -ENOSPC) {
> > -                                     f2fs_bug_on(sbi, 1);
> > -                                     break;
> > -                             }
> > -                     } while (err &&
> > -                             IS_ENABLED(CONFIG_F2FS_FAULT_INJECTION));
> > -                     if (err)
> > +                     err = f2fs_reserve_new_block(&dn);
> > +                     if (err == -ENOSPC)
> > +                             f2fs_bug_on(sbi, 1);
> > +                     else if (err)
> >                               goto err;
> >                       continue;
> >               }
> > @@ -727,15 +722,10 @@ static int do_recover_data(struct f2fs_sb_info *sbi, struct inode *inode,
> >               if (f2fs_is_valid_blkaddr(sbi, dest, META_POR)) {
> >
> >                       if (src == NULL_ADDR) {
> > -                             do {
> > -                                     err = f2fs_reserve_new_block(&dn);
> > -                                     if (err == -ENOSPC) {
> > -                                             f2fs_bug_on(sbi, 1);
> > -                                             break;
> > -                                     }
> > -                             } while (err &&
> > -                                     IS_ENABLED(CONFIG_F2FS_FAULT_INJECTION));
> > -                             if (err)
> > +                             err = f2fs_reserve_new_block(&dn);
> > +                             if (err == -ENOSPC)
> > +                                     f2fs_bug_on(sbi, 1);
> > +                             else if (err)
> >                                       goto err;
> >                       }
> >   retry_prev: