On Monday, 26 of November 2007, Jeremy Fitzhardinge wrote: > 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?
I don't know the details. > Could vfs_check_frozen() be changed to something that is freezer-compatible? That seems doable in principle. I'll have a closer look at it. > >> 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? The freezer will not wait for this particular task. Still, the task will have TIF_FREEZE set, so it will freeze as soon as freezer_count() is reached, unless the thawing of tasks is carried out first. If used in the right place, it's reasonably safe, but we need to know what the right place is. [That's how we handle vfork(), BTW.] > > 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. Not exactly. :-) > 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. Agreed, but the only way to tell the freezer "don't wait for this task", if the task in question is in TASK_UNINTERRUPTIBLE, is to annotate it. Greetings, Rafael - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/