Re: BUG: enabling psacct breaks fsfreeze

From: Jan Kara
Date: Wed Nov 07 2012 - 17:32:36 EST

On Wed 07-11-12 22:21:19, Nikola Ciprich wrote:
> Hello Jan,
>
> tried on 3.7-rc4, works great! thanks!
>
> will You submit as-is, or do You plan any further changes?
> do You plan to backport for stable kernels? I can try it and send for review
> if You want (although we'll have to wait till it's upstream anyways)
Thanks for testing. I've sent the patch and will see what other guys
tell.

Honza

> On Wed, Nov 07, 2012 at 07:51:37PM +0100, Jan Kara wrote:
> > On Thu 01-11-12 23:50:53, Jan Kara wrote:
> > > On Thu 01-11-12 15:23:25, Nikola Ciprich wrote:
> > > > Nov 1 14:23:25 vmnci22 [ 1075.178123] SysRq : Show Blocked State
> > > > Nov 1 14:23:25 vmnci22 [ 1075.180555] task PC stack pid father
> > > > Nov 1 14:23:25 vmnci22 [ 1075.180592] fsfreeze D 0000000000000000 0 4215 4195 0x00000000
> > > > Nov 1 14:23:25 vmnci22 [ 1075.180599] ffff8800090b9b28 0000000000000046 0000000000000000 ffffffff00000000
> > > > Nov 1 14:23:25 vmnci22 [ 1075.180606] 0000000000013780 ffff8800090b9fd8 ffff88000f716170 ffff88000f715e80
> > > > Nov 1 14:23:25 vmnci22 [ 1075.180612] ffff88000f715dc0 ffffffff81566080 ffff88000f716170 000000010002f405
> > > > Nov 1 14:23:25 vmnci22 [ 1075.180619] Call Trace:
> > > > Nov 1 14:23:25 vmnci22 [ 1075.180693] [<ffffffff810e2dbb>] __generic_file_aio_write+0xbb/0x420
> > > > Nov 1 14:23:25 vmnci22 [ 1075.180729] [<ffffffff81079290>] ? autoremove_wake_function+0x0/0x40
> > > > Nov 1 14:23:25 vmnci22 [ 1075.180736] [<ffffffff810e317f>] generic_file_aio_write+0x5f/0xc0
> > > Thanks. So the system isn't really deadlocked. It's just that fsfreeze
> > > command hangs, isn't it? OK, I understand that it's kind of incovenient
> > > situation because every command will hang like this when the filesystem is
> > > frozen.
> > >
> > > Now I only have to come up with a way to improve this... It isn't quite
> > > simple - to properly protect against freezing be have to communicate down
> > > into generic_file_aio_write() that we want to bail out if filesystem is
> > > frozen instead of waiting.
> > OK, can you test attached patch?
> >
> > Honza
> >
> > --
> > Jan Kara <jack@xxxxxxx>
> > SUSE Labs, CR
>
> > From 1cc937c5a850b2f9f0c2a83fdf757911602db198 Mon Sep 17 00:00:00 2001
> > From: Jan Kara <jack@xxxxxxx>
> > Date: Wed, 7 Nov 2012 19:26:45 +0100
> > Subject: [PATCH] fs: Fix hang with BSD accounting on frozen filesystem
> >
> > When BSD process accounting is enabled and logs information to a filesystem
> > which gets frozen, system easily becomes unusable because each attempt to
> > account process information blocks. Thus e.g. every task gets blocked in exit.
> >
> > It seems better to drop accounting information (which can already happen when
> > filesystem is running out of space) instead of locking system up. This is
> > implemented using a special flag FMODE_NO_FREEZE_WAIT in file->f_mode of a
> > file to which accounting information is written.
> >
> > Signed-off-by: Jan Kara <jack@xxxxxxx>
> > ---
> > fs/btrfs/file.c | 3 ++-
> > fs/cifs/file.c | 3 ++-
> > fs/fuse/file.c | 3 ++-
> > fs/ntfs/file.c | 3 ++-
> > fs/ocfs2/file.c | 3 ++-
> > fs/open.c | 2 +-
> > fs/xfs/xfs_file.c | 3 ++-
> > include/linux/fs.h | 14 ++++++++++++++
> > kernel/acct.c | 1 +
> > mm/filemap.c | 3 ++-
> > 10 files changed, 30 insertions(+), 8 deletions(-)
> >
> > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> > index 9ab1bed..6eb2e30 100644
> > --- a/fs/btrfs/file.c
> > +++ b/fs/btrfs/file.c
> > @@ -1411,7 +1411,8 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
> > ssize_t err = 0;
> > size_t count, ocount;
> >
> > - sb_start_write(inode->i_sb);
> > + if (!sb_start_file_write(file))
> > + return -EAGAIN;
> >
> > mutex_lock(&inode->i_mutex);
> >
> > diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> > index edb25b4..1629e47 100644
> > --- a/fs/cifs/file.c
> > +++ b/fs/cifs/file.c
> > @@ -2448,7 +2448,8 @@ cifs_writev(struct kiocb *iocb, const struct iovec *iov,
> >
> > BUG_ON(iocb->ki_pos != pos);
> >
> > - sb_start_write(inode->i_sb);
> > + if (!sb_start_file_write(file))
> > + return -EAGAIN;
> >
> > /*
> > * We need to hold the sem to be sure nobody modifies lock list
> > diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> > index 78d2837..641df9e 100644
> > --- a/fs/fuse/file.c
> > +++ b/fs/fuse/file.c
> > @@ -947,7 +947,8 @@ static ssize_t fuse_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
> > return err;
> >
> > count = ocount;
> > - sb_start_write(inode->i_sb);
> > + if (!sb_start_file_write(file))
> > + return -EAGAIN;
> > mutex_lock(&inode->i_mutex);
> >
> > /* We can write back this queue in page reclaim */
> > diff --git a/fs/ntfs/file.c b/fs/ntfs/file.c
> > index 1ecf464..028b349 100644
> > --- a/fs/ntfs/file.c
> > +++ b/fs/ntfs/file.c
> > @@ -2118,7 +2118,8 @@ static ssize_t ntfs_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
> >
> > BUG_ON(iocb->ki_pos != pos);
> >
> > - sb_start_write(inode->i_sb);
> > + if (!sb_start_file_write(file))
> > + return -EAGAIN;
> > mutex_lock(&inode->i_mutex);
> > ret = ntfs_file_aio_write_nolock(iocb, iov, nr_segs, &iocb->ki_pos);
> > mutex_unlock(&inode->i_mutex);
> > diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
> > index 5a4ee77..93ef34d 100644
> > --- a/fs/ocfs2/file.c
> > +++ b/fs/ocfs2/file.c
> > @@ -2265,7 +2265,8 @@ static ssize_t ocfs2_file_aio_write(struct kiocb *iocb,
> > if (iocb->ki_left == 0)
> > return 0;
> >
> > - sb_start_write(inode->i_sb);
> > + if (!sb_start_file_write(file))
> > + return -EAGAIN;
> >
> > appending = file->f_flags & O_APPEND ? 1 : 0;
> > direct_io = file->f_flags & O_DIRECT ? 1 : 0;
> > diff --git a/fs/open.c b/fs/open.c
> > index 59071f5..42bd875 100644
> > --- a/fs/open.c
> > +++ b/fs/open.c
> > @@ -808,7 +808,7 @@ static inline int build_open_flags(int flags, umode_t mode, struct open_flags *o
> > op->mode = 0;
> >
> > /* Must never be set by userspace */
> > - flags &= ~FMODE_NONOTIFY & ~O_CLOEXEC;
> > + flags &= ~FMODE_NONOTIFY & ~O_CLOEXEC & ~FMODE_NO_FREEZE_WAIT;
> >
> > /*
> > * O_SYNC is implemented as __O_SYNC|O_DSYNC. As many places only
> > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> > index aa473fa..7d8af61 100644
> > --- a/fs/xfs/xfs_file.c
> > +++ b/fs/xfs/xfs_file.c
> > @@ -771,7 +771,8 @@ xfs_file_aio_write(
> > if (ocount == 0)
> > return 0;
> >
> > - sb_start_write(inode->i_sb);
> > + if (!sb_start_file_write(file))
> > + return -EAGAIN;
> >
> > if (XFS_FORCED_SHUTDOWN(ip->i_mount)) {
> > ret = -EIO;
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index b33cfc9..c040a6c 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -123,6 +123,9 @@ typedef void (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
> > /* File was opened by fanotify and shouldn't generate fanotify events */
> > #define FMODE_NONOTIFY ((__force fmode_t)0x1000000)
> >
> > +/* Write to file should fail on frozen fs rather than block */
> > +#define FMODE_NO_FREEZE_WAIT ((__force fmode_t)0x2000000)
> > +
> > /*
> > * Flag for rw_copy_check_uvector and compat_rw_copy_check_uvector
> > * that indicates that they should check the contents of the iovec are
> > @@ -1401,6 +1404,17 @@ static inline int sb_start_write_trylock(struct super_block *sb)
> > return __sb_start_write(sb, SB_FREEZE_WRITE, false);
> > }
> >
> > +/*
> > + * We use trylock semantics if write originates in kernel and normal lock
> > + * semantics otherwise. This is a hack but solves problems with deadlocking
> > + * of e.g. psacct when filesystem is frozen.
> > + */
> > +static inline int sb_start_file_write(struct file *file)
> > +{
> > + return __sb_start_write(file->f_mapping->host->i_sb, SB_FREEZE_WRITE,
> > + !(file->f_mode & FMODE_NO_FREEZE_WAIT));
> > +}
> > +
> > /**
> > * sb_start_pagefault - get write access to a superblock from a page fault
> > * @sb: the super we write to
> > diff --git a/kernel/acct.c b/kernel/acct.c
> > index 051e071..0b5f231 100644
> > --- a/kernel/acct.c
> > +++ b/kernel/acct.c
> > @@ -183,6 +183,7 @@ static void acct_file_reopen(struct bsd_acct_struct *acct, struct file *file,
> > acct->needcheck = jiffies + ACCT_TIMEOUT*HZ;
> > acct->active = 1;
> > list_add(&acct->list, &acct_list);
> > + file->f_mode |= FMODE_NO_FREEZE_WAIT;
> > }
> > if (old_acct) {
> > mnt_unpin(old_acct->f_path.mnt);
> > diff --git a/mm/filemap.c b/mm/filemap.c
> > index 83efee7..3b2812b 100644
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -2527,7 +2527,8 @@ ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
> >
> > BUG_ON(iocb->ki_pos != pos);
> >
> > - sb_start_write(inode->i_sb);
> > + if (!sb_start_file_write(file))
> > + return -EAGAIN;
> > mutex_lock(&inode->i_mutex);
> > ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
> > mutex_unlock(&inode->i_mutex);
> > --
> > 1.7.1
> >
>
>
> --
> -------------------------------------
> Ing. Nikola CIPRICH
> LinuxBox.cz, s.r.o.
> 28. rijna 168, 709 00 Ostrava
>
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>
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> -------------------------------------


--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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