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SubjectRe: [2.4] VFS locking problem during concurrent link/unlink
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On Thu, 2003-01-16 at 11:06, Nikita Danilov wrote:
> Chris Mason writes:
> > On Thu, 2003-01-16 at 10:43, Oleg Drokin wrote:
>
> [...]
>
> >
> > link count at 1
> > reiserfs_link: make new directory entry for link, schedule()
> > reiserfs_unlink: dec link count to zero, remove file stat data
> > reiserfs_link: inc link count, return thinking the stat data is still
> > there
>
> What protects ext2 from doing the same on the SMP?
>

They inc the link count in ext2_link before scheduling. The patch below
is what I had in mind, but is untested.

-chris

--- 1.24/fs/reiserfs/namei.c Fri Aug 9 11:22:33 2002
+++ edited/fs/reiserfs/namei.c Thu Jan 16 11:20:11 2003
@@ -748,6 +748,7 @@
int windex ;
struct reiserfs_transaction_handle th ;
int jbegin_count;
+ unsigned long savelink;

inode = dentry->d_inode;

@@ -783,11 +784,20 @@
inode->i_nlink = 1;
}

+ inode->i_nlink--;
+
+ /*
+ * we schedule before doing the add_save_link call, save the link
+ * count so we don't race
+ */
+ savelink = inode->i_nlink;
+
+
retval = reiserfs_cut_from_item (&th, &path, &(de.de_entry_key), dir, NULL, 0);
- if (retval < 0)
+ if (retval < 0) {
+ inode->i_nlink++;
goto end_unlink;
-
- inode->i_nlink--;
+ }
inode->i_ctime = CURRENT_TIME;
reiserfs_update_sd (&th, inode);

@@ -796,7 +806,7 @@
dir->i_ctime = dir->i_mtime = CURRENT_TIME;
reiserfs_update_sd (&th, dir);

- if (!inode->i_nlink)
+ if (!savelink)
/* prevent file from getting lost */
add_save_link (&th, inode, 0/* not truncate */);

@@ -900,6 +910,12 @@
//FIXME: sd_nlink is 32 bit for new files
return -EMLINK;
}
+ if (inode->i_nlink == 0) {
+ return -ENOENT;
+ }
+
+ /* inc before scheduling so reiserfs_unlink knows we are here */
+ inode->i_nlink++;

journal_begin(&th, dir->i_sb, jbegin_count) ;
windex = push_journal_writer("reiserfs_link") ;
@@ -912,12 +928,12 @@
reiserfs_update_inode_transaction(dir) ;

if (retval) {
+ inode->i_nlink--;
pop_journal_writer(windex) ;
journal_end(&th, dir->i_sb, jbegin_count) ;
return retval;
}

- inode->i_nlink++;
ctime = CURRENT_TIME;
inode->i_ctime = ctime;
reiserfs_update_sd (&th, inode);
@@ -992,6 +1008,7 @@
int jbegin_count ;
umode_t old_inode_mode;
time_t ctime;
+ unsigned long savelink = 1;


/* two balancings: old name removal, new name insertion or "save" link,
@@ -1161,6 +1178,7 @@
} else {
new_dentry_inode->i_nlink--;
}
+ savelink = new_dentry_inode->i_nlink;
ctime = CURRENT_TIME;
new_dentry_inode->i_ctime = ctime;
}
@@ -1196,7 +1214,7 @@
reiserfs_update_sd (&th, new_dir);

if (new_dentry_inode) {
- if (new_dentry_inode->i_nlink == 0)
+ if (savelink == 0)
add_save_link (&th, new_dentry_inode, 0/* not truncate */);
reiserfs_update_sd (&th, new_dentry_inode);
}


-
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