Messages in this thread Patch in this message | | | Date | Fri, 16 Jan 2004 15:10:37 +0530 | From | Maneesh Soni <> | Subject | Re: 2.6.1-mm2: BUG in kswapd? |
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On Thu, Jan 15, 2004 at 08:05:13PM -0800, Walt H wrote: > Hi Maneesh, > > I've had a pretty repeatible case of the BUG in list.h from attempting > backups via rsync. This has persisted thru 2.6.1-mm3. I reverted the > race fix patch at: > > ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.1/2.6.1-mm3/broken-out/sysfs_remove_dir-vs-dcache_readdir-race-fix.patch > > Which allows my rsync to finish properly.
Hi Walt,
This patch is needed for a different race. We get hangs when we read and remove a sysfs directory at the same time on an SMP box. It is easily recreated by running following two loops. (Obviously without this fix)
while true; do insmod drivers/net/dummy.ko; rmmod dummy; done while true; do find /sys/class/net > /dev/null; done
I am still not convinced that this fix will cause any problem.
The kswapd problem what I have understood so far, is happening because of a bad d_child pointer in the dentry. As it is hitting the list_del BUG(), and the only list_del in prune_dcache() is for d_child list pointer. I suspect dentry from d_child list is being deleted more than once.
Can you elaborate on the recreation scenario a little bit more or if possible run this debug patch on top of -mm3. This should print some info about the bad dentry.
Thanks Maneesh
fs/dcache.c | 7 +++++++ 1 files changed, 7 insertions(+)
diff -puN fs/dcache.c~prune_dcache-debug fs/dcache.c --- linux-2.6.1-mm3/fs/dcache.c~prune_dcache-debug 2004-01-16 14:36:00.000000000 +0530 +++ linux-2.6.1-mm3-maneesh/fs/dcache.c 2004-01-16 15:03:25.000000000 +0530 @@ -344,6 +344,13 @@ static inline void prune_one_dentry(stru struct dentry * parent; __d_drop(dentry); + if (dentry->d_child.next->prev != &dentry->d_child) { + printk("Bad dentry for %s flags %lx, %d\n", dentry->d_name.name, + dentry->d_vfs_flags, atomic_read(&dentry->d_count)); + if (dentry->d_sb) + printk("Super block magic %lx\n", dentry->d_sb->s_magic); + BUG(); + } list_del(&dentry->d_child); dentry_stat.nr_dentry--; /* For d_free, below */ dentry_iput(dentry); _ -- Maneesh Soni Linux Technology Center, IBM Software Lab, Bangalore, India email: maneesh@in.ibm.com Phone: 91-80-5044999 Fax: 91-80-5268553 T/L : 9243696 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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