On Tue, Dec 23, 2014 at 04:58:46PM +0800, Chao Yu wrote: > Hi Jaegeuk, > > > -----Original Message----- > > From: Jaegeuk Kim [mailto:jaegeuk@xxxxxxxxxx] > > Sent: Tuesday, December 23, 2014 3:41 PM > > To: Chao Yu > > Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-fsdevel@xxxxxxxxxxxxxxx; > > linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx > > Subject: Re: [f2fs-dev] [PATCH 6/6] f2fs: avoid double lock for cp_rwsem > > > > Hi, > > > > On Tue, Dec 23, 2014 at 03:01:36PM +0800, Chao Yu wrote: > > > Hi Jaegeuk, > > > > > > > -----Original Message----- > > > > From: Jaegeuk Kim [mailto:jaegeuk@xxxxxxxxxx] > > > > Sent: Monday, December 22, 2014 12:35 AM > > > > To: linux-kernel@xxxxxxxxxxxxxxx; linux-fsdevel@xxxxxxxxxxxxxxx; > > > > linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx > > > > Cc: Jaegeuk Kim > > > > Subject: [f2fs-dev] [PATCH 6/6] f2fs: avoid double lock for cp_rwsem > > > > > > > > The __f2fs_add_link is covered by cp_rwsem all the time. > > > > This calls init_inode_metadata, which conducts some acl operations including > > > > memory allocation with GFP_KERNEL previously. > > > > But, under memory pressure, f2fs_write_data_page can be called, which also > > > > grabs cp_mutex too. > > > > > > grabs cp_rwsem. > > > > Got it. > > > > > > > > > Basically, it's safe since down_read was used in both of cases, but it'd > > > > better avoid this situation in advance. > > > > > > If checkpoint intend to hold down_write in the middle of the two down_read > > > caller, it will cause a deadlock, so it's not safe. > > > > What I meant was like this. > > - down_read > > If someone else intends to hold down_write (in checkpoint()) here, > we will encounter deadlock. > > Because this writer will add itself to inner waiter list of spinlock as there > is an exist reader had held this lock, then the following reader will start to > spin as it detect that waiter list is not empty. Then deadlock occurred. Ah ha. I see. :) I'll change the description. Thanks, > > I guess this design can effectively avoid starve for the writer when encounters > a large number of readers. > > Thanks > > > - down_read > > - up_read > > - up_read > > > > This should be safe, right? > > Thanks, > > > > > > > > Could you update the comments? > > > > > > > > > > > Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx> > > > > > > Anyway, Nice catch and please add: > > > > > > Reviewed-by: Chao Yu <chao2.yu@xxxxxxxxxxx> > > > > > > > --- > > > > fs/f2fs/acl.c | 4 ++-- > > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/fs/f2fs/acl.c b/fs/f2fs/acl.c > > > > index 1ccb26b..7f12d28 100644 > > > > --- a/fs/f2fs/acl.c > > > > +++ b/fs/f2fs/acl.c > > > > @@ -62,7 +62,7 @@ static struct posix_acl *f2fs_acl_from_disk(const char *value, size_t > > size) > > > > if (count == 0) > > > > return NULL; > > > > > > > > - acl = posix_acl_alloc(count, GFP_KERNEL); > > > > + acl = posix_acl_alloc(count, GFP_NOFS); > > > > if (!acl) > > > > return ERR_PTR(-ENOMEM); > > > > > > > > @@ -116,7 +116,7 @@ static void *f2fs_acl_to_disk(const struct posix_acl *acl, size_t *size) > > > > int i; > > > > > > > > f2fs_acl = kmalloc(sizeof(struct f2fs_acl_header) + acl->a_count * > > > > - sizeof(struct f2fs_acl_entry), GFP_KERNEL); > > > > + sizeof(struct f2fs_acl_entry), GFP_NOFS); > > > > if (!f2fs_acl) > > > > return ERR_PTR(-ENOMEM); > > > > > > > > -- > > > > 2.1.1 > > > > > > > > > > > > ------------------------------------------------------------------------------ > > > > Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server > > > > from Actuate! Instantly Supercharge Your Business Reports and Dashboards > > > > with Interactivity, Sharing, Native Excel Exports, App Integration & more > > > > Get technology previously reserved for billion-dollar corporations, FREE > > > > http://pubads.g.doubleclick.net/gampad/clk?id=164703151&iu=/4140/ostg.clktrk > > > > _______________________________________________ > > > > Linux-f2fs-devel mailing list > > > > Linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx > > > > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
