Messages in this thread | | | Date | Thu, 27 Jul 2006 19:18:39 +1000 | From | Nick Piggin <> | Subject | Re: [BUG?] possible recursive locking detected |
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Anton Altaparmakov wrote: > On Thu, 2006-07-27 at 00:38 -0700, Andrew Morton wrote: > >>On Thu, 27 Jul 2006 08:15:27 +0100 >>Anton Altaparmakov <aia21@cam.ac.uk> wrote: >> >> >>>>I'm surprised ext2 is allocating with __GFP_FS set, though. Would that >>>>cause any problem? >>> >>>That is an ext2 bug IMO. >> >>There is no bug. >> >>What there is is an ill-defined set of rules. If we want to tighten these >>rules we have a choice between > > > I beg to differ. It is a bug. You cannot reenter the file system when > the file system is trying to allocate memory. Otherwise you can never > allocate memory with any locks held or you are bound to introduce an > A->B B->A deadlock somewhere.
I don't think it is a bug in general. It really depends on the allocation:
- If it is a path that might be required in order to writeout a page, then yes GFP_NOFS is going to help prevent deadlocks.
- If it is a path where you'll take the same locks as page reclaim requires, then again GFP_NOFS is required.
For NTFS case, it seems like holding i_mutex on the write path falls foul of the second problem. But I agree with Andrew that this is a critical case where we do have to enter the fs. GFP_NOFS is too big a hammer to use.
I guess you'd have to change NTFS to do something sane privately, or come up with a nice general solution that doesn't harm the common filesystems that apparently don't have a problem here... can you just add GFP_NOFS to NTFS's mapping_gfp_mask to start with?
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