* [PATCH] xfs: don't call into blockgc scan with freeze protection
@ 2021-02-18 20:14 Brian Foster
2021-02-19 3:23 ` Darrick J. Wong
0 siblings, 1 reply; 6+ messages in thread
From: Brian Foster @ 2021-02-18 20:14 UTC (permalink / raw)
To: linux-xfs; +Cc: djwong
fstest xfs/167 produced a lockdep splat that complained about a
nested transaction acquiring freeze protection during an eofblocks
scan. Drop freeze protection around the block reclaim scan in the
transaction allocation code to avoid this problem.
Signed-off-by: Brian Foster <bfoster@redhat.com>
---
fs/xfs/xfs_trans.c | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)
diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index 44f72c09c203..c32c62d3b77a 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -261,6 +261,7 @@ xfs_trans_alloc(
{
struct xfs_trans *tp;
int error;
+ bool retried = false;
/*
* Allocate the handle before we do our freeze accounting and setting up
@@ -288,19 +289,27 @@ xfs_trans_alloc(
INIT_LIST_HEAD(&tp->t_dfops);
tp->t_firstblock = NULLFSBLOCK;
+retry:
error = xfs_trans_reserve(tp, resp, blocks, rtextents);
- if (error == -ENOSPC) {
+ if (error == -ENOSPC && !retried) {
/*
* We weren't able to reserve enough space for the transaction.
* Flush the other speculative space allocations to free space.
* Do not perform a synchronous scan because callers can hold
* other locks.
*/
+ retried = true;
+ if (!(flags & XFS_TRANS_NO_WRITECOUNT))
+ sb_end_intwrite(mp->m_super);
error = xfs_blockgc_free_space(mp, NULL);
- if (!error)
- error = xfs_trans_reserve(tp, resp, blocks, rtextents);
- }
- if (error) {
+ if (error) {
+ kmem_cache_free(xfs_trans_zone, tp);
+ return error;
+ }
+ if (!(flags & XFS_TRANS_NO_WRITECOUNT))
+ sb_start_intwrite(mp->m_super);
+ goto retry;
+ } else if (error) {
xfs_trans_cancel(tp);
return error;
}
--
2.26.2
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] xfs: don't call into blockgc scan with freeze protection
2021-02-18 20:14 [PATCH] xfs: don't call into blockgc scan with freeze protection Brian Foster
@ 2021-02-19 3:23 ` Darrick J. Wong
2021-02-19 4:56 ` Dave Chinner
0 siblings, 1 reply; 6+ messages in thread
From: Darrick J. Wong @ 2021-02-19 3:23 UTC (permalink / raw)
To: Brian Foster; +Cc: linux-xfs
On Thu, Feb 18, 2021 at 03:14:58PM -0500, Brian Foster wrote:
> fstest xfs/167 produced a lockdep splat that complained about a
> nested transaction acquiring freeze protection during an eofblocks
> scan. Drop freeze protection around the block reclaim scan in the
> transaction allocation code to avoid this problem.
>
> Signed-off-by: Brian Foster <bfoster@redhat.com>
I think it seems reasonable, though I really wish that other patchset to
clean up all the "modify thread state when we start/end transactions"
had landed.
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
--D
> ---
> fs/xfs/xfs_trans.c | 19 ++++++++++++++-----
> 1 file changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> index 44f72c09c203..c32c62d3b77a 100644
> --- a/fs/xfs/xfs_trans.c
> +++ b/fs/xfs/xfs_trans.c
> @@ -261,6 +261,7 @@ xfs_trans_alloc(
> {
> struct xfs_trans *tp;
> int error;
> + bool retried = false;
>
> /*
> * Allocate the handle before we do our freeze accounting and setting up
> @@ -288,19 +289,27 @@ xfs_trans_alloc(
> INIT_LIST_HEAD(&tp->t_dfops);
> tp->t_firstblock = NULLFSBLOCK;
>
> +retry:
> error = xfs_trans_reserve(tp, resp, blocks, rtextents);
> - if (error == -ENOSPC) {
> + if (error == -ENOSPC && !retried) {
> /*
> * We weren't able to reserve enough space for the transaction.
> * Flush the other speculative space allocations to free space.
> * Do not perform a synchronous scan because callers can hold
> * other locks.
> */
> + retried = true;
> + if (!(flags & XFS_TRANS_NO_WRITECOUNT))
> + sb_end_intwrite(mp->m_super);
> error = xfs_blockgc_free_space(mp, NULL);
> - if (!error)
> - error = xfs_trans_reserve(tp, resp, blocks, rtextents);
> - }
> - if (error) {
> + if (error) {
> + kmem_cache_free(xfs_trans_zone, tp);
> + return error;
> + }
> + if (!(flags & XFS_TRANS_NO_WRITECOUNT))
> + sb_start_intwrite(mp->m_super);
> + goto retry;
> + } else if (error) {
> xfs_trans_cancel(tp);
> return error;
> }
> --
> 2.26.2
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] xfs: don't call into blockgc scan with freeze protection
2021-02-19 3:23 ` Darrick J. Wong
@ 2021-02-19 4:56 ` Dave Chinner
2021-02-19 13:09 ` Brian Foster
0 siblings, 1 reply; 6+ messages in thread
From: Dave Chinner @ 2021-02-19 4:56 UTC (permalink / raw)
To: Darrick J. Wong; +Cc: Brian Foster, linux-xfs
On Thu, Feb 18, 2021 at 07:23:09PM -0800, Darrick J. Wong wrote:
> On Thu, Feb 18, 2021 at 03:14:58PM -0500, Brian Foster wrote:
> > fstest xfs/167 produced a lockdep splat that complained about a
> > nested transaction acquiring freeze protection during an eofblocks
> > scan. Drop freeze protection around the block reclaim scan in the
> > transaction allocation code to avoid this problem.
> >
> > Signed-off-by: Brian Foster <bfoster@redhat.com>
>
> I think it seems reasonable, though I really wish that other patchset to
> clean up all the "modify thread state when we start/end transactions"
> had landed.
>
> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
>
> --D
>
> > ---
> > fs/xfs/xfs_trans.c | 19 ++++++++++++++-----
> > 1 file changed, 14 insertions(+), 5 deletions(-)
> >
> > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> > index 44f72c09c203..c32c62d3b77a 100644
> > --- a/fs/xfs/xfs_trans.c
> > +++ b/fs/xfs/xfs_trans.c
> > @@ -261,6 +261,7 @@ xfs_trans_alloc(
> > {
> > struct xfs_trans *tp;
> > int error;
> > + bool retried = false;
> >
> > /*
> > * Allocate the handle before we do our freeze accounting and setting up
> > @@ -288,19 +289,27 @@ xfs_trans_alloc(
> > INIT_LIST_HEAD(&tp->t_dfops);
> > tp->t_firstblock = NULLFSBLOCK;
> >
> > +retry:
> > error = xfs_trans_reserve(tp, resp, blocks, rtextents);
> > - if (error == -ENOSPC) {
> > + if (error == -ENOSPC && !retried) {
> > /*
> > * We weren't able to reserve enough space for the transaction.
> > * Flush the other speculative space allocations to free space.
> > * Do not perform a synchronous scan because callers can hold
> > * other locks.
> > */
> > + retried = true;
> > + if (!(flags & XFS_TRANS_NO_WRITECOUNT))
> > + sb_end_intwrite(mp->m_super);
> > error = xfs_blockgc_free_space(mp, NULL);
> > - if (!error)
> > - error = xfs_trans_reserve(tp, resp, blocks, rtextents);
> > - }
> > - if (error) {
> > + if (error) {
> > + kmem_cache_free(xfs_trans_zone, tp);
> > + return error;
> > + }
This seems dangerous to me. If xfs_trans_reserve() adds anything to
the transaction even if it fails, this will fail to free it. e.g.
xfs_log_reserve() call allocate a ticket and attach it to the
transaction and *then fail*. This code will now leak that ticket.
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] xfs: don't call into blockgc scan with freeze protection
2021-02-19 4:56 ` Dave Chinner
@ 2021-02-19 13:09 ` Brian Foster
2021-02-19 20:42 ` Dave Chinner
0 siblings, 1 reply; 6+ messages in thread
From: Brian Foster @ 2021-02-19 13:09 UTC (permalink / raw)
To: Dave Chinner; +Cc: Darrick J. Wong, linux-xfs
On Fri, Feb 19, 2021 at 03:56:58PM +1100, Dave Chinner wrote:
> On Thu, Feb 18, 2021 at 07:23:09PM -0800, Darrick J. Wong wrote:
> > On Thu, Feb 18, 2021 at 03:14:58PM -0500, Brian Foster wrote:
> > > fstest xfs/167 produced a lockdep splat that complained about a
> > > nested transaction acquiring freeze protection during an eofblocks
> > > scan. Drop freeze protection around the block reclaim scan in the
> > > transaction allocation code to avoid this problem.
> > >
> > > Signed-off-by: Brian Foster <bfoster@redhat.com>
...
> > > fs/xfs/xfs_trans.c | 19 ++++++++++++++-----
> > > 1 file changed, 14 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> > > index 44f72c09c203..c32c62d3b77a 100644
> > > --- a/fs/xfs/xfs_trans.c
> > > +++ b/fs/xfs/xfs_trans.c
...
> > > @@ -288,19 +289,27 @@ xfs_trans_alloc(
> > > INIT_LIST_HEAD(&tp->t_dfops);
> > > tp->t_firstblock = NULLFSBLOCK;
> > >
> > > +retry:
> > > error = xfs_trans_reserve(tp, resp, blocks, rtextents);
> > > - if (error == -ENOSPC) {
> > > + if (error == -ENOSPC && !retried) {
> > > /*
> > > * We weren't able to reserve enough space for the transaction.
> > > * Flush the other speculative space allocations to free space.
> > > * Do not perform a synchronous scan because callers can hold
> > > * other locks.
> > > */
> > > + retried = true;
> > > + if (!(flags & XFS_TRANS_NO_WRITECOUNT))
> > > + sb_end_intwrite(mp->m_super);
> > > error = xfs_blockgc_free_space(mp, NULL);
> > > - if (!error)
> > > - error = xfs_trans_reserve(tp, resp, blocks, rtextents);
> > > - }
> > > - if (error) {
> > > + if (error) {
> > > + kmem_cache_free(xfs_trans_zone, tp);
> > > + return error;
> > > + }
>
> This seems dangerous to me. If xfs_trans_reserve() adds anything to
> the transaction even if it fails, this will fail to free it. e.g.
> xfs_log_reserve() call allocate a ticket and attach it to the
> transaction and *then fail*. This code will now leak that ticket.
>
xfs_trans_reserve() ungrants the log ticket (which frees it, at least in
the allocation case) and disassociates from the transaction on error, so
I don't see how this causes any problems.
Brian
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@fromorbit.com
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] xfs: don't call into blockgc scan with freeze protection
2021-02-19 13:09 ` Brian Foster
@ 2021-02-19 20:42 ` Dave Chinner
2021-02-22 12:05 ` Brian Foster
0 siblings, 1 reply; 6+ messages in thread
From: Dave Chinner @ 2021-02-19 20:42 UTC (permalink / raw)
To: Brian Foster; +Cc: Darrick J. Wong, linux-xfs
On Fri, Feb 19, 2021 at 08:09:32AM -0500, Brian Foster wrote:
> On Fri, Feb 19, 2021 at 03:56:58PM +1100, Dave Chinner wrote:
> > On Thu, Feb 18, 2021 at 07:23:09PM -0800, Darrick J. Wong wrote:
> > > On Thu, Feb 18, 2021 at 03:14:58PM -0500, Brian Foster wrote:
> > > > fstest xfs/167 produced a lockdep splat that complained about a
> > > > nested transaction acquiring freeze protection during an eofblocks
> > > > scan. Drop freeze protection around the block reclaim scan in the
> > > > transaction allocation code to avoid this problem.
> > > >
> > > > Signed-off-by: Brian Foster <bfoster@redhat.com>
> ...
> > > > fs/xfs/xfs_trans.c | 19 ++++++++++++++-----
> > > > 1 file changed, 14 insertions(+), 5 deletions(-)
> > > >
> > > > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> > > > index 44f72c09c203..c32c62d3b77a 100644
> > > > --- a/fs/xfs/xfs_trans.c
> > > > +++ b/fs/xfs/xfs_trans.c
> ...
> > > > @@ -288,19 +289,27 @@ xfs_trans_alloc(
> > > > INIT_LIST_HEAD(&tp->t_dfops);
> > > > tp->t_firstblock = NULLFSBLOCK;
> > > >
> > > > +retry:
> > > > error = xfs_trans_reserve(tp, resp, blocks, rtextents);
> > > > - if (error == -ENOSPC) {
> > > > + if (error == -ENOSPC && !retried) {
> > > > /*
> > > > * We weren't able to reserve enough space for the transaction.
> > > > * Flush the other speculative space allocations to free space.
> > > > * Do not perform a synchronous scan because callers can hold
> > > > * other locks.
> > > > */
> > > > + retried = true;
> > > > + if (!(flags & XFS_TRANS_NO_WRITECOUNT))
> > > > + sb_end_intwrite(mp->m_super);
> > > > error = xfs_blockgc_free_space(mp, NULL);
> > > > - if (!error)
> > > > - error = xfs_trans_reserve(tp, resp, blocks, rtextents);
> > > > - }
> > > > - if (error) {
> > > > + if (error) {
> > > > + kmem_cache_free(xfs_trans_zone, tp);
> > > > + return error;
> > > > + }
> >
> > This seems dangerous to me. If xfs_trans_reserve() adds anything to
> > the transaction even if it fails, this will fail to free it. e.g.
> > xfs_log_reserve() call allocate a ticket and attach it to the
> > transaction and *then fail*. This code will now leak that ticket.
> >
>
> xfs_trans_reserve() ungrants the log ticket (which frees it, at least in
> the allocation case) and disassociates from the transaction on error, so
> I don't see how this causes any problems.
It ungrants the log ticket when it jumps to "undo_log" on error.
When xfs_log_reserve() fails, it jumps to "undo_blocks" and doesn't
ungrant the ticket. Hence potentially leaving an allocated ticket
attached to the transaction on error. xfs_trans_cancel() handles
this just fine, just freeing the transaction doesn't.
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] xfs: don't call into blockgc scan with freeze protection
2021-02-19 20:42 ` Dave Chinner
@ 2021-02-22 12:05 ` Brian Foster
0 siblings, 0 replies; 6+ messages in thread
From: Brian Foster @ 2021-02-22 12:05 UTC (permalink / raw)
To: Dave Chinner; +Cc: Darrick J. Wong, linux-xfs
On Sat, Feb 20, 2021 at 07:42:48AM +1100, Dave Chinner wrote:
> On Fri, Feb 19, 2021 at 08:09:32AM -0500, Brian Foster wrote:
> > On Fri, Feb 19, 2021 at 03:56:58PM +1100, Dave Chinner wrote:
> > > On Thu, Feb 18, 2021 at 07:23:09PM -0800, Darrick J. Wong wrote:
> > > > On Thu, Feb 18, 2021 at 03:14:58PM -0500, Brian Foster wrote:
> > > > > fstest xfs/167 produced a lockdep splat that complained about a
> > > > > nested transaction acquiring freeze protection during an eofblocks
> > > > > scan. Drop freeze protection around the block reclaim scan in the
> > > > > transaction allocation code to avoid this problem.
> > > > >
> > > > > Signed-off-by: Brian Foster <bfoster@redhat.com>
> > ...
> > > > > fs/xfs/xfs_trans.c | 19 ++++++++++++++-----
> > > > > 1 file changed, 14 insertions(+), 5 deletions(-)
> > > > >
> > > > > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> > > > > index 44f72c09c203..c32c62d3b77a 100644
> > > > > --- a/fs/xfs/xfs_trans.c
> > > > > +++ b/fs/xfs/xfs_trans.c
> > ...
> > > > > @@ -288,19 +289,27 @@ xfs_trans_alloc(
> > > > > INIT_LIST_HEAD(&tp->t_dfops);
> > > > > tp->t_firstblock = NULLFSBLOCK;
> > > > >
> > > > > +retry:
> > > > > error = xfs_trans_reserve(tp, resp, blocks, rtextents);
> > > > > - if (error == -ENOSPC) {
> > > > > + if (error == -ENOSPC && !retried) {
> > > > > /*
> > > > > * We weren't able to reserve enough space for the transaction.
> > > > > * Flush the other speculative space allocations to free space.
> > > > > * Do not perform a synchronous scan because callers can hold
> > > > > * other locks.
> > > > > */
> > > > > + retried = true;
> > > > > + if (!(flags & XFS_TRANS_NO_WRITECOUNT))
> > > > > + sb_end_intwrite(mp->m_super);
> > > > > error = xfs_blockgc_free_space(mp, NULL);
> > > > > - if (!error)
> > > > > - error = xfs_trans_reserve(tp, resp, blocks, rtextents);
> > > > > - }
> > > > > - if (error) {
> > > > > + if (error) {
> > > > > + kmem_cache_free(xfs_trans_zone, tp);
> > > > > + return error;
> > > > > + }
> > >
> > > This seems dangerous to me. If xfs_trans_reserve() adds anything to
> > > the transaction even if it fails, this will fail to free it. e.g.
> > > xfs_log_reserve() call allocate a ticket and attach it to the
> > > transaction and *then fail*. This code will now leak that ticket.
> > >
> >
> > xfs_trans_reserve() ungrants the log ticket (which frees it, at least in
> > the allocation case) and disassociates from the transaction on error, so
> > I don't see how this causes any problems.
>
> It ungrants the log ticket when it jumps to "undo_log" on error.
> When xfs_log_reserve() fails, it jumps to "undo_blocks" and doesn't
> ungrant the ticket. Hence potentially leaving an allocated ticket
> attached to the transaction on error. xfs_trans_cancel() handles
> this just fine, just freeing the transaction doesn't.
>
Ah, my mistake. Must have misread the label...
Brian
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@fromorbit.com
>
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-02-22 12:06 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
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2021-02-18 20:14 [PATCH] xfs: don't call into blockgc scan with freeze protection Brian Foster
2021-02-19 3:23 ` Darrick J. Wong
2021-02-19 4:56 ` Dave Chinner
2021-02-19 13:09 ` Brian Foster
2021-02-19 20:42 ` Dave Chinner
2021-02-22 12:05 ` Brian Foster
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