Messages in this thread | | | Date | Mon, 26 Nov 2007 10:44:20 -0800 | From | Jeremy Fitzhardinge <> | Subject | Re: freeze vs freezer |
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Rafael J. Wysocki wrote: > On Thursday, 22 of November 2007, Jeremy Fitzhardinge wrote: > >> It seems that a process blocked in a write to an xfs filesystem due to >> xfs_freeze cannot be frozen by the freezer. >> > > The freezer doesn't handle tasks in TASK_UNINTERRUPTIBLE and I don't know how > to make it handle them without at least partially defeating its purpose. >
Well, I guess the question is whether an xfs-frozen writer really needs to be UNINTERRUPTIBLE from the freezer's perspective (clearly it does from usermode's perspective - filesystem writes just don't return EINTR).
From a quick poke around, it looks to me like freezing is actually implemented in the VFS layer rather than in XFS itself: is that right? Could vfs_check_frozen() be changed to something that is freezer-compatible?
>> I see this if I suspend my laptop while doing something xfs-filesystem >> intensive, like a kernel build. My suspend scripts freeze the XFS >> filesystem (as Dave said I should), which presumably blocks some writer, >> and then the freezer times out and fails to complete. >> >> Here's part of the process dump the freezer does when it times out: >> >> cc1 D 00000000 0 18138 18137 >> dd5f1e24 00200082 00000002 00000000 ecdeeb00 ecdeec64 c200f280 00000001 >> 009c09a0 dd5f1e0c dd5f1e0c 0000000f 00000000 00000000 00000000 dd5f1e74 >> c7beb480 dd5f1e88 dd5f1ea8 c0228d97 e8889540 dd5f1e38 c015b75d dd5f1e44 >> Call Trace: >> [<c0228d97>] xfs_write+0xf4/0x6d9 >> [<c0226038>] xfs_file_aio_write+0x53/0x5b >> [<c0171c15>] do_sync_write+0xae/0xec >> [<c0172343>] vfs_write+0xa4/0x120 >> [<c01728d7>] sys_write+0x3b/0x60 >> [<c0106fae>] sysenter_past_esp+0x6b/0xa1 >> ======================= >> >> >> I haven't looked at how to fix this yet. I only just worked out why I >> was getting suspend failures. >> > > Well, you can add freezer_do_not_count()/freezer_count() annotations to > xfs_write() (and whatever else is blocked as a result of the XFS being frozen). >
What would be the implications of that? Would that just prevent freezing while there's something blocked there?
> Generally, that would be risky without the freezing of XFS, however, because it > might leak us filesystem data to a storage device after creating a hibernation > image which would result in the filesystem corruption after the resume. > > Still, if you only suspend to RAM, that should be safe. >
I specifically added it because I was getting data loss due to crashes during suspend/resume problems. It's been pretty stable lately, but I may as well remove the xfs_freeze from my suspend scripts if this is the solution.
I think the broader issue is that there's no reason in principle why something blocked due to xfs-freezing (or vfs freezing) should prevent the freezer from completing.
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