There could be a potential deadlock when the storage capacity
is almost full and theren't enough free segments available, due
to which FG_GC is needed in the atomic commit ioctl as shown in
the below callstack -
schedule_timeout
io_schedule_timeout
congestion_wait
f2fs_drop_inmem_pages_all
f2fs_gc
f2fs_balance_fs
__write_node_page
f2fs_fsync_node_pages
f2fs_do_sync_file
f2fs_ioctl
If this inode doesn't have i_gc_failures[GC_FAILURE_ATOMIC] set,
then it waits forever in f2fs_drop_inmem_pages_all(), for this
atomic inode to be dropped. And the rest of the system is stuck
waiting for sbi->gc_mutex lock, which is acquired by f2fs_balance_fs()
in the stack above.
Signed-off-by: Sahitya Tummala <[email protected]>
---
fs/f2fs/segment.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index da830fc..335ec09 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -300,7 +300,8 @@ void f2fs_drop_inmem_pages_all(struct f2fs_sb_info *sbi, bool gc_failure)
if (inode) {
if (gc_failure) {
- if (fi->i_gc_failures[GC_FAILURE_ATOMIC])
+ if (fi->i_gc_failures[GC_FAILURE_ATOMIC] ||
+ F2FS_I(inode)->inmem_task == current)
goto drop;
goto skip;
}
--
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
On 2019/11/8 19:03, Sahitya Tummala wrote:
> There could be a potential deadlock when the storage capacity
> is almost full and theren't enough free segments available, due
> to which FG_GC is needed in the atomic commit ioctl as shown in
> the below callstack -
>
> schedule_timeout
> io_schedule_timeout
> congestion_wait
> f2fs_drop_inmem_pages_all
> f2fs_gc
> f2fs_balance_fs
> __write_node_page
> f2fs_fsync_node_pages
> f2fs_do_sync_file
> f2fs_ioctl
>
> If this inode doesn't have i_gc_failures[GC_FAILURE_ATOMIC] set,
> then it waits forever in f2fs_drop_inmem_pages_all(), for this
> atomic inode to be dropped. And the rest of the system is stuck
> waiting for sbi->gc_mutex lock, which is acquired by f2fs_balance_fs()
> in the stack above.
I think the root cause of this issue is there is potential infinite loop in
f2fs_drop_inmem_pages_all() for the case of gc_failure is true, because once the
first inode in inode_list[ATOMIC_FILE] list didn't suffer gc failure, we will
skip dropping its in-memory cache and calling iput(), and traverse the list
again, most possibly there is the same inode in the head of that list.
Could you please check below fix:
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 7bf7b0194944..8a3a35b42a37 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1395,6 +1395,7 @@ struct f2fs_sb_info {
unsigned int gc_mode; /* current GC state */
unsigned int next_victim_seg[2]; /* next segment in victim section */
/* for skip statistic */
+ unsigned int atomic_files; /* # of opened atomic file */
unsigned long long skipped_atomic_files[2]; /* FG_GC and BG_GC */
unsigned long long skipped_gc_rwsem; /* FG_GC only */
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index ecd063239642..79f4b348951a 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -2047,6 +2047,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
if (list_empty(&fi->inmem_ilist))
list_add_tail(&fi->inmem_ilist, &sbi->inode_list[ATOMIC_FILE]);
+ sbi->atomic_files++;
spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
/* add inode in inmem_list first and set atomic_file */
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 8b977bbd6822..6aa0bb693697 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -288,6 +288,8 @@ void f2fs_drop_inmem_pages_all(struct f2fs_sb_info *sbi,
bool gc_failure)
struct list_head *head = &sbi->inode_list[ATOMIC_FILE];
struct inode *inode;
struct f2fs_inode_info *fi;
+ unsigned int count = sbi->atomic_files;
+ unsigned int looped = 0;
next:
spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
if (list_empty(head)) {
@@ -296,22 +298,29 @@ void f2fs_drop_inmem_pages_all(struct f2fs_sb_info *sbi,
bool gc_failure)
}
fi = list_first_entry(head, struct f2fs_inode_info, inmem_ilist);
inode = igrab(&fi->vfs_inode);
+ if (inode)
+ list_move_tail(&fi->inmem_ilist, head);
spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
if (inode) {
if (gc_failure) {
- if (fi->i_gc_failures[GC_FAILURE_ATOMIC])
- goto drop;
- goto skip;
+ if (!fi->i_gc_failures[GC_FAILURE_ATOMIC])
+ goto skip;
}
-drop:
set_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
f2fs_drop_inmem_pages(inode);
+skip:
iput(inode);
}
-skip:
+
congestion_wait(BLK_RW_ASYNC, HZ/50);
cond_resched();
+
+ if (gc_failure) {
+ if (++looped >= count)
+ return;
+ }
+
goto next;
}
@@ -334,6 +343,7 @@ void f2fs_drop_inmem_pages(struct inode *inode)
spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
if (!list_empty(&fi->inmem_ilist))
list_del_init(&fi->inmem_ilist);
+ sbi->atomic_files--;
spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
}
Thanks,
Hi Chao,
On Mon, Nov 11, 2019 at 10:51:10AM +0800, Chao Yu wrote:
> On 2019/11/8 19:03, Sahitya Tummala wrote:
> > There could be a potential deadlock when the storage capacity
> > is almost full and theren't enough free segments available, due
> > to which FG_GC is needed in the atomic commit ioctl as shown in
> > the below callstack -
> >
> > schedule_timeout
> > io_schedule_timeout
> > congestion_wait
> > f2fs_drop_inmem_pages_all
> > f2fs_gc
> > f2fs_balance_fs
> > __write_node_page
> > f2fs_fsync_node_pages
> > f2fs_do_sync_file
> > f2fs_ioctl
> >
> > If this inode doesn't have i_gc_failures[GC_FAILURE_ATOMIC] set,
> > then it waits forever in f2fs_drop_inmem_pages_all(), for this
> > atomic inode to be dropped. And the rest of the system is stuck
> > waiting for sbi->gc_mutex lock, which is acquired by f2fs_balance_fs()
> > in the stack above.
>
> I think the root cause of this issue is there is potential infinite loop in
> f2fs_drop_inmem_pages_all() for the case of gc_failure is true, because once the
> first inode in inode_list[ATOMIC_FILE] list didn't suffer gc failure, we will
> skip dropping its in-memory cache and calling iput(), and traverse the list
> again, most possibly there is the same inode in the head of that list.
>
I thought we are expecting for those atomic updates (without any gc failures) to be
committed by doing congestion_wait() and thus retrying again. Hence, I just
fixed only if we are ending up waiting for commit to happen in the atomic
commit path itself, which will be a deadlock.
> Could you please check below fix:
>
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 7bf7b0194944..8a3a35b42a37 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -1395,6 +1395,7 @@ struct f2fs_sb_info {
> unsigned int gc_mode; /* current GC state */
> unsigned int next_victim_seg[2]; /* next segment in victim section */
> /* for skip statistic */
> + unsigned int atomic_files; /* # of opened atomic file */
> unsigned long long skipped_atomic_files[2]; /* FG_GC and BG_GC */
> unsigned long long skipped_gc_rwsem; /* FG_GC only */
>
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index ecd063239642..79f4b348951a 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -2047,6 +2047,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
> if (list_empty(&fi->inmem_ilist))
> list_add_tail(&fi->inmem_ilist, &sbi->inode_list[ATOMIC_FILE]);
> + sbi->atomic_files++;
> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>
> /* add inode in inmem_list first and set atomic_file */
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 8b977bbd6822..6aa0bb693697 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -288,6 +288,8 @@ void f2fs_drop_inmem_pages_all(struct f2fs_sb_info *sbi,
> bool gc_failure)
> struct list_head *head = &sbi->inode_list[ATOMIC_FILE];
> struct inode *inode;
> struct f2fs_inode_info *fi;
> + unsigned int count = sbi->atomic_files;
If the sbi->atomic_files decrements just after this, then the below exit condition
may not work. In that case, looped will never be >= count.
> + unsigned int looped = 0;
> next:
> spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
> if (list_empty(head)) {
> @@ -296,22 +298,29 @@ void f2fs_drop_inmem_pages_all(struct f2fs_sb_info *sbi,
> bool gc_failure)
> }
> fi = list_first_entry(head, struct f2fs_inode_info, inmem_ilist);
> inode = igrab(&fi->vfs_inode);
> + if (inode)
> + list_move_tail(&fi->inmem_ilist, head);
> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>
> if (inode) {
> if (gc_failure) {
> - if (fi->i_gc_failures[GC_FAILURE_ATOMIC])
> - goto drop;
> - goto skip;
> + if (!fi->i_gc_failures[GC_FAILURE_ATOMIC])
> + goto skip;
> }
> -drop:
> set_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
> f2fs_drop_inmem_pages(inode);
> +skip:
> iput(inode);
Does this result into f2fs_evict_inode() in this context for this inode?
thanks,
> }
> -skip:
> +
> congestion_wait(BLK_RW_ASYNC, HZ/50);
> cond_resched();
> +
> + if (gc_failure) {
> + if (++looped >= count)
> + return;
> + }
> +
> goto next;
> }
>
> @@ -334,6 +343,7 @@ void f2fs_drop_inmem_pages(struct inode *inode)
> spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
> if (!list_empty(&fi->inmem_ilist))
> list_del_init(&fi->inmem_ilist);
> + sbi->atomic_files--;
> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
> }
>
> Thanks,
--
--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
Hi Sahitya,
On 2019/11/11 11:40, Sahitya Tummala wrote:
> Hi Chao,
>
> On Mon, Nov 11, 2019 at 10:51:10AM +0800, Chao Yu wrote:
>> On 2019/11/8 19:03, Sahitya Tummala wrote:
>>> There could be a potential deadlock when the storage capacity
>>> is almost full and theren't enough free segments available, due
>>> to which FG_GC is needed in the atomic commit ioctl as shown in
>>> the below callstack -
>>>
>>> schedule_timeout
>>> io_schedule_timeout
>>> congestion_wait
>>> f2fs_drop_inmem_pages_all
>>> f2fs_gc
>>> f2fs_balance_fs
>>> __write_node_page
>>> f2fs_fsync_node_pages
>>> f2fs_do_sync_file
>>> f2fs_ioctl
>>>
>>> If this inode doesn't have i_gc_failures[GC_FAILURE_ATOMIC] set,
>>> then it waits forever in f2fs_drop_inmem_pages_all(), for this
>>> atomic inode to be dropped. And the rest of the system is stuck
>>> waiting for sbi->gc_mutex lock, which is acquired by f2fs_balance_fs()
>>> in the stack above.
>>
>> I think the root cause of this issue is there is potential infinite loop in
>> f2fs_drop_inmem_pages_all() for the case of gc_failure is true, because once the
>> first inode in inode_list[ATOMIC_FILE] list didn't suffer gc failure, we will
>> skip dropping its in-memory cache and calling iput(), and traverse the list
>> again, most possibly there is the same inode in the head of that list.
>>
>
> I thought we are expecting for those atomic updates (without any gc failures) to be
> committed by doing congestion_wait() and thus retrying again. Hence, I just
Nope, we only need to drop inode which encounter gc failures, and keep the rest
inodes.
> fixed only if we are ending up waiting for commit to happen in the atomic
> commit path itself, which will be a deadlock.
Look into call stack you provide, I don't think it's correct to drop such inode,
as its dirty pages should be committed before f2fs_fsync_node_pages(), so
calling f2fs_drop_inmem_pages won't release any inmem pages, and won't help
looped GC caused by skipping due to inmem pages.
And then I figure out below fix...
>
>> Could you please check below fix:
>>
>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>> index 7bf7b0194944..8a3a35b42a37 100644
>> --- a/fs/f2fs/f2fs.h
>> +++ b/fs/f2fs/f2fs.h
>> @@ -1395,6 +1395,7 @@ struct f2fs_sb_info {
>> unsigned int gc_mode; /* current GC state */
>> unsigned int next_victim_seg[2]; /* next segment in victim section */
>> /* for skip statistic */
>> + unsigned int atomic_files; /* # of opened atomic file */
>> unsigned long long skipped_atomic_files[2]; /* FG_GC and BG_GC */
>> unsigned long long skipped_gc_rwsem; /* FG_GC only */
>>
>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>> index ecd063239642..79f4b348951a 100644
>> --- a/fs/f2fs/file.c
>> +++ b/fs/f2fs/file.c
>> @@ -2047,6 +2047,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>> spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
>> if (list_empty(&fi->inmem_ilist))
>> list_add_tail(&fi->inmem_ilist, &sbi->inode_list[ATOMIC_FILE]);
>> + sbi->atomic_files++;
>> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>>
>> /* add inode in inmem_list first and set atomic_file */
>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>> index 8b977bbd6822..6aa0bb693697 100644
>> --- a/fs/f2fs/segment.c
>> +++ b/fs/f2fs/segment.c
>> @@ -288,6 +288,8 @@ void f2fs_drop_inmem_pages_all(struct f2fs_sb_info *sbi,
>> bool gc_failure)
>> struct list_head *head = &sbi->inode_list[ATOMIC_FILE];
>> struct inode *inode;
>> struct f2fs_inode_info *fi;
>> + unsigned int count = sbi->atomic_files;
>
> If the sbi->atomic_files decrements just after this, then the below exit condition
> may not work. In that case, looped will never be >= count.
>
>> + unsigned int looped = 0;
>> next:
>> spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
>> if (list_empty(head)) {
>> @@ -296,22 +298,29 @@ void f2fs_drop_inmem_pages_all(struct f2fs_sb_info *sbi,
>> bool gc_failure)
>> }
>> fi = list_first_entry(head, struct f2fs_inode_info, inmem_ilist);
>> inode = igrab(&fi->vfs_inode);
>> + if (inode)
>> + list_move_tail(&fi->inmem_ilist, head);
>> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>>
>> if (inode) {
>> if (gc_failure) {
>> - if (fi->i_gc_failures[GC_FAILURE_ATOMIC])
>> - goto drop;
>> - goto skip;
>> + if (!fi->i_gc_failures[GC_FAILURE_ATOMIC])
>> + goto skip;
>> }
>> -drop:
>> set_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
>> f2fs_drop_inmem_pages(inode);
>> +skip:
>> iput(inode);
>
> Does this result into f2fs_evict_inode() in this context for this inode?
Yup, we need to call igrab/iput in pair in f2fs_drop_inmem_pages_all() anyway.
Previously, we may have .i_count leak...
Thanks,
>
> thanks,
>
>> }
>> -skip:
>> +
>> congestion_wait(BLK_RW_ASYNC, HZ/50);
>> cond_resched();
>> +
>> + if (gc_failure) {
>> + if (++looped >= count)
>> + return;
>> + }
>> +
>> goto next;
>> }
>>
>> @@ -334,6 +343,7 @@ void f2fs_drop_inmem_pages(struct inode *inode)
>> spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
>> if (!list_empty(&fi->inmem_ilist))
>> list_del_init(&fi->inmem_ilist);
>> + sbi->atomic_files--;
>> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>> }
>>
>> Thanks,
>
Hi Chao,
On Mon, Nov 11, 2019 at 02:28:47PM +0800, Chao Yu wrote:
> Hi Sahitya,
>
> On 2019/11/11 11:40, Sahitya Tummala wrote:
> > Hi Chao,
> >
> > On Mon, Nov 11, 2019 at 10:51:10AM +0800, Chao Yu wrote:
> >> On 2019/11/8 19:03, Sahitya Tummala wrote:
> >>> There could be a potential deadlock when the storage capacity
> >>> is almost full and theren't enough free segments available, due
> >>> to which FG_GC is needed in the atomic commit ioctl as shown in
> >>> the below callstack -
> >>>
> >>> schedule_timeout
> >>> io_schedule_timeout
> >>> congestion_wait
> >>> f2fs_drop_inmem_pages_all
> >>> f2fs_gc
> >>> f2fs_balance_fs
> >>> __write_node_page
> >>> f2fs_fsync_node_pages
> >>> f2fs_do_sync_file
> >>> f2fs_ioctl
> >>>
> >>> If this inode doesn't have i_gc_failures[GC_FAILURE_ATOMIC] set,
> >>> then it waits forever in f2fs_drop_inmem_pages_all(), for this
> >>> atomic inode to be dropped. And the rest of the system is stuck
> >>> waiting for sbi->gc_mutex lock, which is acquired by f2fs_balance_fs()
> >>> in the stack above.
> >>
> >> I think the root cause of this issue is there is potential infinite loop in
> >> f2fs_drop_inmem_pages_all() for the case of gc_failure is true, because once the
> >> first inode in inode_list[ATOMIC_FILE] list didn't suffer gc failure, we will
> >> skip dropping its in-memory cache and calling iput(), and traverse the list
> >> again, most possibly there is the same inode in the head of that list.
> >>
> >
> > I thought we are expecting for those atomic updates (without any gc failures) to be
> > committed by doing congestion_wait() and thus retrying again. Hence, I just
>
> Nope, we only need to drop inode which encounter gc failures, and keep the rest
> inodes.
>
> > fixed only if we are ending up waiting for commit to happen in the atomic
> > commit path itself, which will be a deadlock.
>
> Look into call stack you provide, I don't think it's correct to drop such inode,
> as its dirty pages should be committed before f2fs_fsync_node_pages(), so
> calling f2fs_drop_inmem_pages won't release any inmem pages, and won't help
> looped GC caused by skipping due to inmem pages.
>
> And then I figure out below fix...
>
Thanks for the explanation.
The fix below looks good to me.
Thanks,
Sahitya.
> >
> >> Could you please check below fix:
> >>
> >> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >> index 7bf7b0194944..8a3a35b42a37 100644
> >> --- a/fs/f2fs/f2fs.h
> >> +++ b/fs/f2fs/f2fs.h
> >> @@ -1395,6 +1395,7 @@ struct f2fs_sb_info {
> >> unsigned int gc_mode; /* current GC state */
> >> unsigned int next_victim_seg[2]; /* next segment in victim section */
> >> /* for skip statistic */
> >> + unsigned int atomic_files; /* # of opened atomic file */
> >> unsigned long long skipped_atomic_files[2]; /* FG_GC and BG_GC */
> >> unsigned long long skipped_gc_rwsem; /* FG_GC only */
> >>
> >> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> >> index ecd063239642..79f4b348951a 100644
> >> --- a/fs/f2fs/file.c
> >> +++ b/fs/f2fs/file.c
> >> @@ -2047,6 +2047,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> >> spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
> >> if (list_empty(&fi->inmem_ilist))
> >> list_add_tail(&fi->inmem_ilist, &sbi->inode_list[ATOMIC_FILE]);
> >> + sbi->atomic_files++;
> >> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
> >>
> >> /* add inode in inmem_list first and set atomic_file */
> >> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >> index 8b977bbd6822..6aa0bb693697 100644
> >> --- a/fs/f2fs/segment.c
> >> +++ b/fs/f2fs/segment.c
> >> @@ -288,6 +288,8 @@ void f2fs_drop_inmem_pages_all(struct f2fs_sb_info *sbi,
> >> bool gc_failure)
> >> struct list_head *head = &sbi->inode_list[ATOMIC_FILE];
> >> struct inode *inode;
> >> struct f2fs_inode_info *fi;
> >> + unsigned int count = sbi->atomic_files;
> >
> > If the sbi->atomic_files decrements just after this, then the below exit condition
> > may not work. In that case, looped will never be >= count.
> >
> >> + unsigned int looped = 0;
> >> next:
> >> spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
> >> if (list_empty(head)) {
> >> @@ -296,22 +298,29 @@ void f2fs_drop_inmem_pages_all(struct f2fs_sb_info *sbi,
> >> bool gc_failure)
> >> }
> >> fi = list_first_entry(head, struct f2fs_inode_info, inmem_ilist);
> >> inode = igrab(&fi->vfs_inode);
> >> + if (inode)
> >> + list_move_tail(&fi->inmem_ilist, head);
> >> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
> >>
> >> if (inode) {
> >> if (gc_failure) {
> >> - if (fi->i_gc_failures[GC_FAILURE_ATOMIC])
> >> - goto drop;
> >> - goto skip;
> >> + if (!fi->i_gc_failures[GC_FAILURE_ATOMIC])
> >> + goto skip;
> >> }
> >> -drop:
> >> set_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
> >> f2fs_drop_inmem_pages(inode);
> >> +skip:
> >> iput(inode);
> >
> > Does this result into f2fs_evict_inode() in this context for this inode?
>
> Yup, we need to call igrab/iput in pair in f2fs_drop_inmem_pages_all() anyway.
>
> Previously, we may have .i_count leak...
>
> Thanks,
>
> >
> > thanks,
> >
> >> }
> >> -skip:
> >> +
> >> congestion_wait(BLK_RW_ASYNC, HZ/50);
> >> cond_resched();
> >> +
> >> + if (gc_failure) {
> >> + if (++looped >= count)
> >> + return;
> >> + }
> >> +
> >> goto next;
> >> }
> >>
> >> @@ -334,6 +343,7 @@ void f2fs_drop_inmem_pages(struct inode *inode)
> >> spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
> >> if (!list_empty(&fi->inmem_ilist))
> >> list_del_init(&fi->inmem_ilist);
> >> + sbi->atomic_files--;
> >> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
> >> }
> >>
> >> Thanks,
> >
--
--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
Hi Sahitya,
On 2019/11/11 14:44, Sahitya Tummala wrote:
> Hi Chao,
>
> On Mon, Nov 11, 2019 at 02:28:47PM +0800, Chao Yu wrote:
>> Hi Sahitya,
>>
>> On 2019/11/11 11:40, Sahitya Tummala wrote:
>>> Hi Chao,
>>>
>>> On Mon, Nov 11, 2019 at 10:51:10AM +0800, Chao Yu wrote:
>>>> On 2019/11/8 19:03, Sahitya Tummala wrote:
>>>>> There could be a potential deadlock when the storage capacity
>>>>> is almost full and theren't enough free segments available, due
>>>>> to which FG_GC is needed in the atomic commit ioctl as shown in
>>>>> the below callstack -
>>>>>
>>>>> schedule_timeout
>>>>> io_schedule_timeout
>>>>> congestion_wait
>>>>> f2fs_drop_inmem_pages_all
>>>>> f2fs_gc
>>>>> f2fs_balance_fs
>>>>> __write_node_page
>>>>> f2fs_fsync_node_pages
>>>>> f2fs_do_sync_file
>>>>> f2fs_ioctl
>>>>>
>>>>> If this inode doesn't have i_gc_failures[GC_FAILURE_ATOMIC] set,
>>>>> then it waits forever in f2fs_drop_inmem_pages_all(), for this
>>>>> atomic inode to be dropped. And the rest of the system is stuck
>>>>> waiting for sbi->gc_mutex lock, which is acquired by f2fs_balance_fs()
>>>>> in the stack above.
>>>>
>>>> I think the root cause of this issue is there is potential infinite loop in
>>>> f2fs_drop_inmem_pages_all() for the case of gc_failure is true, because once the
>>>> first inode in inode_list[ATOMIC_FILE] list didn't suffer gc failure, we will
>>>> skip dropping its in-memory cache and calling iput(), and traverse the list
>>>> again, most possibly there is the same inode in the head of that list.
>>>>
>>>
>>> I thought we are expecting for those atomic updates (without any gc failures) to be
>>> committed by doing congestion_wait() and thus retrying again. Hence, I just
>>
>> Nope, we only need to drop inode which encounter gc failures, and keep the rest
>> inodes.
>>
>>> fixed only if we are ending up waiting for commit to happen in the atomic
>>> commit path itself, which will be a deadlock.
>>
>> Look into call stack you provide, I don't think it's correct to drop such inode,
>> as its dirty pages should be committed before f2fs_fsync_node_pages(), so
>> calling f2fs_drop_inmem_pages won't release any inmem pages, and won't help
>> looped GC caused by skipping due to inmem pages.
>>
>> And then I figure out below fix...
>>
>
> Thanks for the explanation.
> The fix below looks good to me.
So could you submit v2? :)
Thanks,
>
> Thanks,
> Sahitya.
>
>>>
>>>> Could you please check below fix:
>>>>
>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>> index 7bf7b0194944..8a3a35b42a37 100644
>>>> --- a/fs/f2fs/f2fs.h
>>>> +++ b/fs/f2fs/f2fs.h
>>>> @@ -1395,6 +1395,7 @@ struct f2fs_sb_info {
>>>> unsigned int gc_mode; /* current GC state */
>>>> unsigned int next_victim_seg[2]; /* next segment in victim section */
>>>> /* for skip statistic */
>>>> + unsigned int atomic_files; /* # of opened atomic file */
>>>> unsigned long long skipped_atomic_files[2]; /* FG_GC and BG_GC */
>>>> unsigned long long skipped_gc_rwsem; /* FG_GC only */
>>>>
>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>>> index ecd063239642..79f4b348951a 100644
>>>> --- a/fs/f2fs/file.c
>>>> +++ b/fs/f2fs/file.c
>>>> @@ -2047,6 +2047,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>>>> spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
>>>> if (list_empty(&fi->inmem_ilist))
>>>> list_add_tail(&fi->inmem_ilist, &sbi->inode_list[ATOMIC_FILE]);
>>>> + sbi->atomic_files++;
>>>> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>>>>
>>>> /* add inode in inmem_list first and set atomic_file */
>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>>> index 8b977bbd6822..6aa0bb693697 100644
>>>> --- a/fs/f2fs/segment.c
>>>> +++ b/fs/f2fs/segment.c
>>>> @@ -288,6 +288,8 @@ void f2fs_drop_inmem_pages_all(struct f2fs_sb_info *sbi,
>>>> bool gc_failure)
>>>> struct list_head *head = &sbi->inode_list[ATOMIC_FILE];
>>>> struct inode *inode;
>>>> struct f2fs_inode_info *fi;
>>>> + unsigned int count = sbi->atomic_files;
>>>
>>> If the sbi->atomic_files decrements just after this, then the below exit condition
>>> may not work. In that case, looped will never be >= count.
>>>
>>>> + unsigned int looped = 0;
>>>> next:
>>>> spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
>>>> if (list_empty(head)) {
>>>> @@ -296,22 +298,29 @@ void f2fs_drop_inmem_pages_all(struct f2fs_sb_info *sbi,
>>>> bool gc_failure)
>>>> }
>>>> fi = list_first_entry(head, struct f2fs_inode_info, inmem_ilist);
>>>> inode = igrab(&fi->vfs_inode);
>>>> + if (inode)
>>>> + list_move_tail(&fi->inmem_ilist, head);
>>>> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>>>>
>>>> if (inode) {
>>>> if (gc_failure) {
>>>> - if (fi->i_gc_failures[GC_FAILURE_ATOMIC])
>>>> - goto drop;
>>>> - goto skip;
>>>> + if (!fi->i_gc_failures[GC_FAILURE_ATOMIC])
>>>> + goto skip;
>>>> }
>>>> -drop:
>>>> set_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
>>>> f2fs_drop_inmem_pages(inode);
>>>> +skip:
>>>> iput(inode);
>>>
>>> Does this result into f2fs_evict_inode() in this context for this inode?
>>
>> Yup, we need to call igrab/iput in pair in f2fs_drop_inmem_pages_all() anyway.
>>
>> Previously, we may have .i_count leak...
>>
>> Thanks,
>>
>>>
>>> thanks,
>>>
>>>> }
>>>> -skip:
>>>> +
>>>> congestion_wait(BLK_RW_ASYNC, HZ/50);
>>>> cond_resched();
>>>> +
>>>> + if (gc_failure) {
>>>> + if (++looped >= count)
>>>> + return;
>>>> + }
>>>> +
>>>> goto next;
>>>> }
>>>>
>>>> @@ -334,6 +343,7 @@ void f2fs_drop_inmem_pages(struct inode *inode)
>>>> spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
>>>> if (!list_empty(&fi->inmem_ilist))
>>>> list_del_init(&fi->inmem_ilist);
>>>> + sbi->atomic_files--;
>>>> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>>>> }
>>>>
>>>> Thanks,
>>>
>