From: Eric Sandeen Subject: Re: [PATCH] replaced BUG() with return -EIO from ext4_ext_get_blocks Date: Fri, 11 Dec 2009 14:02:58 -0600 Message-ID: <4B22A572.5010201@redhat.com> References: <1260540418-11844-1-git-send-email-surbhi.palande@canonical.com> <1260554859.21896.8.camel@bobble.smo.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Surbhi Palande , linux-ext4@vger.kernel.org To: Frank Mayhar Return-path: Received: from mx1.redhat.com ([209.132.183.28]:31431 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760988AbZLKUC7 (ORCPT ); Fri, 11 Dec 2009 15:02:59 -0500 In-Reply-To: <1260554859.21896.8.camel@bobble.smo.corp.google.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: Frank Mayhar wrote: > On Fri, 2009-12-11 at 16:06 +0200, Surbhi Palande wrote: >> This patch fixes the upstream bug# 14286. When the address of an extent >> corresponding to a given block is NULL and the tree is being traversed for >> fetching such an address, a -EIO should be reported instead of a BUG(). This >> situation should normally not occur. However if it does, then the system >> should be rendered usable. >> >> Signed-off-by: Surbhi Palande >> --- >> fs/ext4/extents.c | 7 ++++++- >> 1 files changed, 6 insertions(+), 1 deletions(-) >> >> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c >> index 3a7928f..51f87f3 100644 >> --- a/fs/ext4/extents.c >> +++ b/fs/ext4/extents.c >> @@ -3190,7 +3190,12 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode, >> * this situation is possible, though, _during_ tree modification; >> * this is why assert can't be put in ext4_ext_find_extent() >> */ >> - BUG_ON(path[depth].p_ext == NULL && depth != 0); >> + if (path[depth].p_ext == NULL && depth != 0) { >> + err = -EIO; >> + printk(KERN_ERR "\n ext4 fs error in %s,%s,%s while reading a block ", \ >> + __FILE__, __func__, __LINE__); >> + goto out2; >> + } >> eh = path[depth].p_hdr; >> >> ex = path[depth].p_ext; > > As it happens, I fixed this locally but, as I considered it a band-aid > fix at the time, I never pushed it to you guys. My version of the fix > is below; it dumps more information before returning the EIO. I don't > have a strong preference between the two versions but I would like to > see the commentary included and the extra information is often useful > during debugging. My first thought was that this was a bandaid too, but I guess it can come about due to on-disk corruption for any reason, so it should be handled gracefully, and I suppose this approach seems fine. I think the original plan was that a BUG() should be primarily for things that would arise from a programming error, though EIO & graceful shutdown even for that class of errors would probably be best. Since this is catching on-disk corruption, though, it'd be better to call ext4_error() and let the mount-time error-handling policy decide what to do. I like having more info but below seems awfully wordy ;) Maybe the first printk would suffice, and switching it to an ext4_error() would be best, I think. -Eric > Signed-off-by: Frank Mayhar > > fs/ext4/extents.c | 18 +++++++++++++++++- > 1 files changed, 17 insertions(+), 1 deletions(-) > > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c > index f7bdd55..7aa0bf6 100644 > --- a/fs/ext4/extents.c > +++ b/fs/ext4/extents.c > @@ -2859,8 +2859,24 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode, > * consistent leaf must not be empty; > * this situation is possible, though, _during_ tree modification; > * this is why assert can't be put in ext4_ext_find_extent() > + * > + * We don't want to panic in this case, as it can lead to a crash > + * loop; instead we want to catch the error and abort. > */ > - BUG_ON(path[depth].p_ext == NULL && depth != 0); > + if (path[depth].p_ext == NULL && depth != 0) { > + printk(KERN_ERR > + "EXT4-fs (%s): corrupt extent node ino %lu iblock %d" > + " depth %d pblock %lld\n", > + inode->i_sb->s_id, inode->i_ino, iblock, depth, > + path[depth].p_block); > + if (!path[depth].p_hdr) > + path[depth].p_hdr = ext_block_hdr(path[depth].p_bh); > + printk(KERN_ERR "EXT4-fs (%s): eh_entries %d eh_max %d\n", > + inode->i_sb->s_id, path[depth].p_hdr->eh_entries, > + path[depth].p_hdr->eh_max); > + err = -EIO; > + goto out2; > + } > eh = path[depth].p_hdr; > > ex = path[depth].p_ext;