| Message ID | 20200709083333.137927-2-wqu@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2,1/2] btrfs: avoid possible signal interruption for btrfs_drop_snapshot() on relocation tree | expand |
On Thu, Jul 09, 2020 at 04:33:33PM +0800, Qu Wenruo wrote: > Since most metadata reservation calls can return -EINTR when get > interruped by fatal signal, we need to review the all the metadata > reservation call sites. > > In relocation code, the metadata reservation happens in the following > sites: > - btrfs_block_rsv_refill() in merge_reloc_root() > merge_reloc_root() is a pretty critial section, we don't want get > interrupted by signal, so change the flush status to > BTRFS_RESERVE_FLUSH_LIMIT, so it won't get interrupted by signal. > Since such change can be ENPSPC-prone, also shrink the amount of > metadata to reserve a little to avoid deadly ENOSPC there. > > - btrfs_block_rsv_refill() in reserve_metadata_space() > It calls with BTRFS_RESERVE_FLUSH_LIMIT, which won't get interrupred > by signal. This semantics of BTRFS_RESERVE_FLUSH_LIMIT regarding signals should be documented, right now there's a comment but says something about avoidig deadlocks. > - btrfs_block_rsv_refill() in prepare_to_relocate() > - btrfs_block_rsv_add() in prepare_to_relocate() > - btrfs_block_rsv_refill() in relocate_block_group() > - btrfs_delalloc_reserve_metadata() in relocate_file_extent_cluster() > - btrfs_start_transaction() in relocate_block_group() > - btrfs_start_transaction() in create_reloc_inode() > Can be interruped by fatal signal and we can handle it easily. > For these call sites, just catch the -EINTR value in btrfs_balance() > and count them as canceled. > > Signed-off-by: Qu Wenruo <wqu@suse.com> > --- > fs/btrfs/relocation.c | 13 +++++++++++-- > fs/btrfs/volumes.c | 2 +- > 2 files changed, 12 insertions(+), 3 deletions(-) > > diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c > index 2b869fb2e62c..23914edd4710 100644 > --- a/fs/btrfs/relocation.c > +++ b/fs/btrfs/relocation.c > @@ -1686,12 +1686,21 @@ static noinline_for_stack int merge_reloc_root(struct reloc_control *rc, > btrfs_unlock_up_safe(path, 0); > } > > - min_reserved = fs_info->nodesize * (BTRFS_MAX_LEVEL - 1) * 2; > + /* > + * In merge_reloc_root(), we modify the upper level pointer to swap > + * the tree blocks between reloc tree and subvolume tree. > + * Thus for tree block COW, we COW at most from level 1 to root level > + * for each tree. > + * > + * Thus the needed metadata space is at most root_level * nodesize, > + * and * 2 since we have two trees to COW. > + */ > + min_reserved = fs_info->nodesize * btrfs_root_level(root_item) * 2; > memset(&next_key, 0, sizeof(next_key)); > > while (1) { > ret = btrfs_block_rsv_refill(root, rc->block_rsv, min_reserved, > - BTRFS_RESERVE_FLUSH_ALL); > + BTRFS_RESERVE_FLUSH_LIMIT); > if (ret) { > err = ret; > goto out; > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c > index aabc6c922e04..d60df30bdc47 100644 > --- a/fs/btrfs/volumes.c > +++ b/fs/btrfs/volumes.c > @@ -4135,7 +4135,7 @@ int btrfs_balance(struct btrfs_fs_info *fs_info, > mutex_lock(&fs_info->balance_mutex); > if (ret == -ECANCELED && atomic_read(&fs_info->balance_pause_req)) > btrfs_info(fs_info, "balance: paused"); > - else if (ret == -ECANCELED && atomic_read(&fs_info->balance_cancel_req)) > + else if (ret == -ECANCELED || ret == -EINTR) Why do you remove atomic_read(&fs_info->balance_cancel_req) ? > btrfs_info(fs_info, "balance: canceled"); I'm not sure if it would be useful to print the reason, like - 'canceled: user request' - 'canceled: interrupted' > else > btrfs_info(fs_info, "balance: ended with status: %d", ret); > -- > 2.27.0
On 2020/7/9 下午5:54, David Sterba wrote: > On Thu, Jul 09, 2020 at 04:33:33PM +0800, Qu Wenruo wrote: >> Since most metadata reservation calls can return -EINTR when get >> interruped by fatal signal, we need to review the all the metadata >> reservation call sites. >> >> In relocation code, the metadata reservation happens in the following >> sites: >> - btrfs_block_rsv_refill() in merge_reloc_root() >> merge_reloc_root() is a pretty critial section, we don't want get >> interrupted by signal, so change the flush status to >> BTRFS_RESERVE_FLUSH_LIMIT, so it won't get interrupted by signal. >> Since such change can be ENPSPC-prone, also shrink the amount of >> metadata to reserve a little to avoid deadly ENOSPC there. >> >> - btrfs_block_rsv_refill() in reserve_metadata_space() >> It calls with BTRFS_RESERVE_FLUSH_LIMIT, which won't get interrupred >> by signal. > > This semantics of BTRFS_RESERVE_FLUSH_LIMIT regarding signals should be > documented, right now there's a comment but says something about avoidig > deadlocks. > >> - btrfs_block_rsv_refill() in prepare_to_relocate() >> - btrfs_block_rsv_add() in prepare_to_relocate() >> - btrfs_block_rsv_refill() in relocate_block_group() >> - btrfs_delalloc_reserve_metadata() in relocate_file_extent_cluster() >> - btrfs_start_transaction() in relocate_block_group() >> - btrfs_start_transaction() in create_reloc_inode() >> Can be interruped by fatal signal and we can handle it easily. >> For these call sites, just catch the -EINTR value in btrfs_balance() >> and count them as canceled. >> >> Signed-off-by: Qu Wenruo <wqu@suse.com> >> --- >> fs/btrfs/relocation.c | 13 +++++++++++-- >> fs/btrfs/volumes.c | 2 +- >> 2 files changed, 12 insertions(+), 3 deletions(-) >> >> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c >> index 2b869fb2e62c..23914edd4710 100644 >> --- a/fs/btrfs/relocation.c >> +++ b/fs/btrfs/relocation.c >> @@ -1686,12 +1686,21 @@ static noinline_for_stack int merge_reloc_root(struct reloc_control *rc, >> btrfs_unlock_up_safe(path, 0); >> } >> >> - min_reserved = fs_info->nodesize * (BTRFS_MAX_LEVEL - 1) * 2; >> + /* >> + * In merge_reloc_root(), we modify the upper level pointer to swap >> + * the tree blocks between reloc tree and subvolume tree. >> + * Thus for tree block COW, we COW at most from level 1 to root level >> + * for each tree. >> + * >> + * Thus the needed metadata space is at most root_level * nodesize, >> + * and * 2 since we have two trees to COW. >> + */ >> + min_reserved = fs_info->nodesize * btrfs_root_level(root_item) * 2; >> memset(&next_key, 0, sizeof(next_key)); >> >> while (1) { >> ret = btrfs_block_rsv_refill(root, rc->block_rsv, min_reserved, >> - BTRFS_RESERVE_FLUSH_ALL); >> + BTRFS_RESERVE_FLUSH_LIMIT); >> if (ret) { >> err = ret; >> goto out; >> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c >> index aabc6c922e04..d60df30bdc47 100644 >> --- a/fs/btrfs/volumes.c >> +++ b/fs/btrfs/volumes.c >> @@ -4135,7 +4135,7 @@ int btrfs_balance(struct btrfs_fs_info *fs_info, >> mutex_lock(&fs_info->balance_mutex); >> if (ret == -ECANCELED && atomic_read(&fs_info->balance_pause_req)) >> btrfs_info(fs_info, "balance: paused"); >> - else if (ret == -ECANCELED && atomic_read(&fs_info->balance_cancel_req)) >> + else if (ret == -ECANCELED || ret == -EINTR) > > Why do you remove atomic_read(&fs_info->balance_cancel_req) ? Because now btrfs_should_cancel_balance() can return ECANCELED without balance_cancel_req increased due to pending fatal signal. > >> btrfs_info(fs_info, "balance: canceled"); > > I'm not sure if it would be useful to print the reason, like > > - 'canceled: user request' > - 'canceled: interrupted' To me, if user interrupt the balance progress, it's obvious they want to cancel it. Thus no need to distinguish btrfs balance cancel and signal cancel. Thanks, Qu > >> else >> btrfs_info(fs_info, "balance: ended with status: %d", ret); >> -- >> 2.27.0
On Thu, Jul 09, 2020 at 06:15:09PM +0800, Qu Wenruo wrote: > On 2020/7/9 下午5:54, David Sterba wrote: > > On Thu, Jul 09, 2020 at 04:33:33PM +0800, Qu Wenruo wrote: > >> @@ -4135,7 +4135,7 @@ int btrfs_balance(struct btrfs_fs_info *fs_info, > >> mutex_lock(&fs_info->balance_mutex); > >> if (ret == -ECANCELED && atomic_read(&fs_info->balance_pause_req)) > >> btrfs_info(fs_info, "balance: paused"); > >> - else if (ret == -ECANCELED && atomic_read(&fs_info->balance_cancel_req)) > >> + else if (ret == -ECANCELED || ret == -EINTR) > > > > Why do you remove atomic_read(&fs_info->balance_cancel_req) ? > > Because now btrfs_should_cancel_balance() can return ECANCELED without > balance_cancel_req increased due to pending fatal signal. Ah right, I misread it as || which would remove one reason for cancellation.
On 2020/7/9 下午5:54, David Sterba wrote: > On Thu, Jul 09, 2020 at 04:33:33PM +0800, Qu Wenruo wrote: >> Since most metadata reservation calls can return -EINTR when get >> interruped by fatal signal, we need to review the all the metadata >> reservation call sites. >> >> In relocation code, the metadata reservation happens in the following >> sites: >> - btrfs_block_rsv_refill() in merge_reloc_root() >> merge_reloc_root() is a pretty critial section, we don't want get >> interrupted by signal, so change the flush status to >> BTRFS_RESERVE_FLUSH_LIMIT, so it won't get interrupted by signal. >> Since such change can be ENPSPC-prone, also shrink the amount of >> metadata to reserve a little to avoid deadly ENOSPC there. >> >> - btrfs_block_rsv_refill() in reserve_metadata_space() >> It calls with BTRFS_RESERVE_FLUSH_LIMIT, which won't get interrupred >> by signal. > > This semantics of BTRFS_RESERVE_FLUSH_LIMIT regarding signals should be > documented, right now there's a comment but says something about avoidig > deadlocks. For this, I tend to add one or more patches to add some comment for all FLUSH enums, and all their callers. I hate when some infrastructure hit me by surprise, and since ticketing system is hidden from a lot of functions, we also need to mention that -EINTR case. Thanks, Qu > >> - btrfs_block_rsv_refill() in prepare_to_relocate() >> - btrfs_block_rsv_add() in prepare_to_relocate() >> - btrfs_block_rsv_refill() in relocate_block_group() >> - btrfs_delalloc_reserve_metadata() in relocate_file_extent_cluster() >> - btrfs_start_transaction() in relocate_block_group() >> - btrfs_start_transaction() in create_reloc_inode() >> Can be interruped by fatal signal and we can handle it easily. >> For these call sites, just catch the -EINTR value in btrfs_balance() >> and count them as canceled. >> >> Signed-off-by: Qu Wenruo <wqu@suse.com> >> --- >> fs/btrfs/relocation.c | 13 +++++++++++-- >> fs/btrfs/volumes.c | 2 +- >> 2 files changed, 12 insertions(+), 3 deletions(-) >> >> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c >> index 2b869fb2e62c..23914edd4710 100644 >> --- a/fs/btrfs/relocation.c >> +++ b/fs/btrfs/relocation.c >> @@ -1686,12 +1686,21 @@ static noinline_for_stack int merge_reloc_root(struct reloc_control *rc, >> btrfs_unlock_up_safe(path, 0); >> } >> >> - min_reserved = fs_info->nodesize * (BTRFS_MAX_LEVEL - 1) * 2; >> + /* >> + * In merge_reloc_root(), we modify the upper level pointer to swap >> + * the tree blocks between reloc tree and subvolume tree. >> + * Thus for tree block COW, we COW at most from level 1 to root level >> + * for each tree. >> + * >> + * Thus the needed metadata space is at most root_level * nodesize, >> + * and * 2 since we have two trees to COW. >> + */ >> + min_reserved = fs_info->nodesize * btrfs_root_level(root_item) * 2; >> memset(&next_key, 0, sizeof(next_key)); >> >> while (1) { >> ret = btrfs_block_rsv_refill(root, rc->block_rsv, min_reserved, >> - BTRFS_RESERVE_FLUSH_ALL); >> + BTRFS_RESERVE_FLUSH_LIMIT); >> if (ret) { >> err = ret; >> goto out; >> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c >> index aabc6c922e04..d60df30bdc47 100644 >> --- a/fs/btrfs/volumes.c >> +++ b/fs/btrfs/volumes.c >> @@ -4135,7 +4135,7 @@ int btrfs_balance(struct btrfs_fs_info *fs_info, >> mutex_lock(&fs_info->balance_mutex); >> if (ret == -ECANCELED && atomic_read(&fs_info->balance_pause_req)) >> btrfs_info(fs_info, "balance: paused"); >> - else if (ret == -ECANCELED && atomic_read(&fs_info->balance_cancel_req)) >> + else if (ret == -ECANCELED || ret == -EINTR) > > Why do you remove atomic_read(&fs_info->balance_cancel_req) ? > >> btrfs_info(fs_info, "balance: canceled"); > > I'm not sure if it would be useful to print the reason, like > > - 'canceled: user request' > - 'canceled: interrupted' > >> else >> btrfs_info(fs_info, "balance: ended with status: %d", ret); >> -- >> 2.27.0
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c index 2b869fb2e62c..23914edd4710 100644 --- a/fs/btrfs/relocation.c +++ b/fs/btrfs/relocation.c @@ -1686,12 +1686,21 @@ static noinline_for_stack int merge_reloc_root(struct reloc_control *rc, btrfs_unlock_up_safe(path, 0); } - min_reserved = fs_info->nodesize * (BTRFS_MAX_LEVEL - 1) * 2; + /* + * In merge_reloc_root(), we modify the upper level pointer to swap + * the tree blocks between reloc tree and subvolume tree. + * Thus for tree block COW, we COW at most from level 1 to root level + * for each tree. + * + * Thus the needed metadata space is at most root_level * nodesize, + * and * 2 since we have two trees to COW. + */ + min_reserved = fs_info->nodesize * btrfs_root_level(root_item) * 2; memset(&next_key, 0, sizeof(next_key)); while (1) { ret = btrfs_block_rsv_refill(root, rc->block_rsv, min_reserved, - BTRFS_RESERVE_FLUSH_ALL); + BTRFS_RESERVE_FLUSH_LIMIT); if (ret) { err = ret; goto out; diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index aabc6c922e04..d60df30bdc47 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -4135,7 +4135,7 @@ int btrfs_balance(struct btrfs_fs_info *fs_info, mutex_lock(&fs_info->balance_mutex); if (ret == -ECANCELED && atomic_read(&fs_info->balance_pause_req)) btrfs_info(fs_info, "balance: paused"); - else if (ret == -ECANCELED && atomic_read(&fs_info->balance_cancel_req)) + else if (ret == -ECANCELED || ret == -EINTR) btrfs_info(fs_info, "balance: canceled"); else btrfs_info(fs_info, "balance: ended with status: %d", ret);
Since most metadata reservation calls can return -EINTR when get interruped by fatal signal, we need to review the all the metadata reservation call sites. In relocation code, the metadata reservation happens in the following sites: - btrfs_block_rsv_refill() in merge_reloc_root() merge_reloc_root() is a pretty critial section, we don't want get interrupted by signal, so change the flush status to BTRFS_RESERVE_FLUSH_LIMIT, so it won't get interrupted by signal. Since such change can be ENPSPC-prone, also shrink the amount of metadata to reserve a little to avoid deadly ENOSPC there. - btrfs_block_rsv_refill() in reserve_metadata_space() It calls with BTRFS_RESERVE_FLUSH_LIMIT, which won't get interrupred by signal. - btrfs_block_rsv_refill() in prepare_to_relocate() - btrfs_block_rsv_add() in prepare_to_relocate() - btrfs_block_rsv_refill() in relocate_block_group() - btrfs_delalloc_reserve_metadata() in relocate_file_extent_cluster() - btrfs_start_transaction() in relocate_block_group() - btrfs_start_transaction() in create_reloc_inode() Can be interruped by fatal signal and we can handle it easily. For these call sites, just catch the -EINTR value in btrfs_balance() and count them as canceled. Signed-off-by: Qu Wenruo <wqu@suse.com> --- fs/btrfs/relocation.c | 13 +++++++++++-- fs/btrfs/volumes.c | 2 +- 2 files changed, 12 insertions(+), 3 deletions(-)