On Thu, 8 Nov 2012, Zach Brown wrote: > Date: Thu, 8 Nov 2012 13:52:33 -0800 > From: Zach Brown <zab@xxxxxxxxxx> > To: Lukas Czerner <lczerner@xxxxxxxxxx> > Cc: linux-ext4@xxxxxxxxxxxxxxx, tytso@xxxxxxx > Subject: Re: [PATCH] ext4: Prevent race while waling extent tree > > On Thu, Nov 08, 2012 at 12:08:49PM +0100, Lukas Czerner wrote: > > + down_read(&EXT4_I(inode)->i_data_sem); > > error = ext4_ext_walk_space(inode, start_blk, len_blks, > > ext4_ext_fiemap_cb, fieinfo); > > + up_read(&EXT4_I(inode)->i_data_sem); > > Can this deadlock? ext4_ext_fiemap_cb() seems to be doing all kinds of > exciting things that might also try and acquire the i_data_sem, like > GFP_KERNEL allocs (reclaim -> writepage) and copying to userspace (mmap > fault -> readpage -> get blocks). > > It seems like the safer fix is to broaden the sampling lock coverage to > include referencing all the extent data but to release it around the > callback. > > No? > > - z Yeah, you're right. Having the lock around the whole ext4_ext_walk_space() might deadlock. I'll fix this. Thanks for noticing this! -Lukas -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
