I wasn't sure if f2fs_setxattr() needed the lock or not, since the call
path from f2fs_xattr_set_acl() doesn't take one anywhere. My first thought
was to move the lock over to the acl code and remove it from here.
Russ
On Mon, Sep 9, 2013 at 7:59 PM, Jaegeuk Kim <[email protected]> wrote:
> Hi,
>
> 2013-09-07 (토), 08:00 +0000, Chao Yu:
> > Hi Knize,
> >
> > Thanks for your reply, I think it's actually meaningless that it's
> > being named after "spin_lock",
> > it's better to rename this spinlock to "round_robin_lock".
> >
> > This patch can only resolve the issue of unbalanced fs_lock usage,
> > it can not fix the deadlock issue.
> > can we fix deadlock issue through this method:
> >
> > - vfs_create()
> > - f2fs_create() - takes an fs_lock and save current thread info into
> > thread_info[NR_GLOBAL_LOCKS]
> > - f2fs_add_link()
> > - __f2fs_add_link()
> > - init_inode_metadata()
> > - f2fs_init_security()
> > - security_inode_init_security()
> > - f2fs_initxattrs()
> > - f2fs_setxattr() - get fs_lock only if there is no current
> > thread info in thread_info
> >
> > So it keeps one thread can only hold one fs_lock to avoid deadlock.
> > Can we use this solution?
>
> It could be.
> But, I think we can avoid to grab the fs_lock at the f2fs_initxattrs()
> level, since this case only happens when f2fs_initxattrs() is called.
> Let's think about ut in more detail.
> Thanks,
>
> >
> >
> >
> > thanks again!
> >
> >
> >
> > ------- Original Message -------
> >
> > Sender : Russ Knize<[email protected]>
> >
> > Date : 九月 07, 2013 04:25 (GMT+09:00)
> >
> > Title : Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better
> > performance
> >
> >
> >
> > I encountered this same issue recently and solved it in much the same
> > way. Can we rename "spin_lock" to something more meaningful?
> >
> >
> > This race actually exposed a potential deadlock between f2fs_create()
> > and f2fs_initxattrs():
> >
> >
> > - vfs_create()
> > - f2fs_create() - takes an fs_lock
> > - f2fs_add_link()
> > - __f2fs_add_link()
> > - init_inode_metadata()
> > - f2fs_init_security()
> > - security_inode_init_security()
> > - f2fs_initxattrs()
> > - f2fs_setxattr() - also takes an fs_lock
> >
> >
> > If another CPU happens to have the same lock that f2fs_setxattr() was
> > trying to take because of the race around next_lock_num, we can get
> > into a deadlock situation if the two threads are also contending over
> > another resource (like bdi).
> >
> >
> > Another scenario is if the above happens while another thread is in
> > the middle of grabbing all of the locks via mutex_lock_all().
> > f2fs_create() is holding a lock that mutex_lock_all() is waiting for
> > and mutex_lock_all() is holding a lock that f2fs_setxattr() is waiting
> > for.
> >
> >
> > Russ
> >
> >
> > On Fri, Sep 6, 2013 at 4:48 AM, Chao Yu <[email protected]> wrote:
> > Hi Kim:
> >
> > I think there is a performance problem: when all
> > sbi->fs_lock is holded,
> >
> > then all other threads may get the same next_lock value from
> > sbi->next_lock_num in function mutex_lock_op,
> >
> > and wait to get the same lock at position fs_lock[next_lock],
> > it unbalance the fs_lock usage.
> >
> > It may lost performance when we do the multithread test.
> >
> >
> >
> > Here is the patch to fix this problem:
> >
> >
> >
> > Signed-off-by: Yu Chao <[email protected]>
> >
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >
> > old mode 100644
> >
> > new mode 100755
> >
> > index 467d42d..983bb45
> >
> > --- a/fs/f2fs/f2fs.h
> >
> > +++ b/fs/f2fs/f2fs.h
> >
> > @@ -371,6 +371,7 @@ struct f2fs_sb_info {
> >
> > struct mutex fs_lock[NR_GLOBAL_LOCKS]; /* blocking FS
> > operations */
> >
> > struct mutex node_write; /* locking
> > node writes */
> >
> > struct mutex writepages; /* mutex for
> > writepages() */
> >
> > + spinlock_t spin_lock; /* lock for
> > next_lock_num */
> >
> > unsigned char next_lock_num; /* round-robin
> > global locks */
> >
> > int por_doing; /* recovery is
> > doing or not */
> >
> > int on_build_free_nids; /*
> > build_free_nids is doing */
> >
> > @@ -533,15 +534,19 @@ static inline void
> > mutex_unlock_all(struct f2fs_sb_info *sbi)
> >
> >
> >
> > static inline int mutex_lock_op(struct f2fs_sb_info *sbi)
> >
> > {
> >
> > - unsigned char next_lock = sbi->next_lock_num %
> > NR_GLOBAL_LOCKS;
> >
> > + unsigned char next_lock;
> >
> > int i = 0;
> >
> >
> >
> > for (; i < NR_GLOBAL_LOCKS; i++)
> >
> > if (mutex_trylock(&sbi->fs_lock[i]))
> >
> > return i;
> >
> >
> >
> > - mutex_lock(&sbi->fs_lock[next_lock]);
> >
> > + spin_lock(&sbi->spin_lock);
> >
> > + next_lock = sbi->next_lock_num % NR_GLOBAL_LOCKS;
> >
> > sbi->next_lock_num++;
> >
> > + spin_unlock(&sbi->spin_lock);
> >
> > +
> >
> > + mutex_lock(&sbi->fs_lock[next_lock]);
> >
> > return next_lock;
> >
> > }
> >
> >
> >
> > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> >
> > old mode 100644
> >
> > new mode 100755
> >
> > index 75c7dc3..4f27596
> >
> > --- a/fs/f2fs/super.c
> >
> > +++ b/fs/f2fs/super.c
> >
> > @@ -657,6 +657,7 @@ static int f2fs_fill_super(struct
> > super_block *sb, void *data, int silent)
> >
> > mutex_init(&sbi->cp_mutex);
> >
> > for (i = 0; i < NR_GLOBAL_LOCKS; i++)
> >
> > mutex_init(&sbi->fs_lock[i]);
> >
> > + spin_lock_init(&sbi->spin_lock);
> >
> > mutex_init(&sbi->node_write);
> >
> > sbi->por_doing = 0;
> >
> > spin_lock_init(&sbi->stat_lock);
> >
> > (END)
> >
> >
> >
> >
> >
> >
> >
> >
> ------------------------------------------------------------------------------
> > Learn the latest--Visual Studio 2012, SharePoint 2013, SQL
> > 2012, more!
> > Discover the easy way to master current and previous Microsoft
> > technologies
> > and advance your career. Get an incredible 1,500+ hours of
> > step-by-step
> > tutorial videos with LearnDevNow. Subscribe today and save!
> >
> http://pubads.g.doubleclick.net/gampad/clk?id=58041391&iu=/4140/ostg.clktrk
> > _______________________________________________
> > Linux-f2fs-devel mailing list
> > [email protected]
> > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
>
> --
> Jaegeuk Kim
> Samsung
>
>
------------------------------------------------------------------------------
How ServiceNow helps IT people transform IT departments:
1. Consolidate legacy IT systems to a single system of record for IT
2. Standardize and globalize service processes across IT
3. Implement zero-touch automation to replace manual, redundant tasks
http://pubads.g.doubleclick.net/gampad/clk?id=51271111&iu=/4140/ostg.clktrk
_______________________________________________
Linux-f2fs-devel mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
