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Message-Id: <20080704091349.BAA2.KOSAKI.MOTOHIRO@jp.fujitsu.com> Date: Fri, 04 Jul 2008 14:40:29 +0900 From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> To: Hugh Dickins <hugh@...itas.com> Cc: kosaki.motohiro@...fujitsu.com, Li Zefan <lizf@...fujitsu.com>, Andrew Morton <akpm@...ux-foundation.org>, LKML <linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, npiggin@...e.de, Lee Schermerhorn <Lee.Schermerhorn@...com>, Rik Van Riel <riel@...hat.com> Subject: Re: [-mm] BUG: sleeping function called from invalid context at include/linux/pagemap.h:290 > > > Could you explain detail of reproduce way? > > > > Nothing special. I booted the system up, and entered KDE, and opened xterm, > > and typed "dmesg". > > > > .config attached. > > The reason you're seeing it and others not is because your > CONFIG_HIGHPTE=y > is making the issue visible. > > __munlock_pte_handler is trying to lock_page (or migration_entry_wait) > while using the per-cpu kmap_atomic from walk_pte_range's pte_offset_map. > Sleeping functions called from atomic context. > > There's quite a lot to worry about there. Wow, this is obiously bug ;-) IMHO, CONFIG_UNEVICTABLE was developed aiming at 64bit. (had depend on 64BIT ago) So, noboy tested it long time on 32bit. Yes, it is definitly bad. I'll fix soon (hopefully). > That page table walker was originally written to gather some info > for /proc display, not to act upon the page table contents in any > serious way. So it's just doing pte_offset_map when every(?) other > page table walk would be required to pte_offset_map_lock. If it > were doing pte_offset_map_lock, then lots more people would have > seen the problem sooner. > > Does this usage need to pte_offset_map_lock? I think to the extent > that it needs to lock_page, it needs to pte_offset_map_lock: both > are because file truncation (or more commonly reclaim, but without > looking into it too carefully, I dare say reclaim isn't a problem > in this context) could interfere with page->mapping and pte at any > instant. > > Conveniently, we have not one but two attempts at a generic page > walker (sigh!): the other one, apply_to_page_range in mm/memory.c, > does do the lock; it also allocates a page table if it's not there, > I guess that aspect wouldn't be a problem on an mlocked area. Maybe > using apply_to_page_range would be better here, and sidestep the > issue of not having CONFIG_PAGE_WALKER. > > But if it does pte_offset_map_lock, look, migration_entry_wait does > so too; well, never mind the lock, it'll kunmap_atomic > Obviously that part cries out for refactoring. > > And how do you manage the lock_page? Offhand, I don't know, I'm > just reporting on the obvious. Would trylocking be good enough? > > (I do dislike "generic page walkers" because they encourage this > kind of oversight; and I hate to think of the latency problems > they might be introducing - no sign of a cond_resched in either.) Thank you great explain. but we can't use trylock because munlock should turn off PAGE_MLOCK at that time. __munlock_pte_handler introduced for avoid PROT_NONE problem. (get_user_pages() can't get PROT_NONE page, old implementation can't munlock PROT_NONE page) So, We had 2 choice 1. enhance get_use_pages() 2. use pagewalk current implementation select 2. Unfortunately this is problematic choice. Now, We have problem on CONFIG_HIGHPTE and !CONFIG_MMU environment. So, I am gradually charmed by choice 1. my fix plan is below 1. CONFIG_UNEVICTABLE depend on 64BIT (just temporary hotfix) 2. add vm_flags ignoring option to get_user_pages() 3. rewrite __munlock_vma_pages_range by new get_user_pages() 4. revert 1 5. revert pagewalker's Kconfig change (someone dislike "select" expression) and Step1 patch is attached below. this patch solve this problem temporary. Li-san, Could you try to below patch on your environment? ---------------------- pagewalk use pte_offset_map(). pte_offset_map() use kmap_atomic(). __munlock_pte_handler() use lock_page(). So, in CONFIG_HIGHPTE=y, following error happend. BUG: sleeping function called from invalid context at include/linux/pagemap.h:290 in_atomic():1, irqs_disabled():0 no locks held by gpg-agent/2134. Pid: 2134, comm: gpg-agent Not tainted 2.6.26-rc8-mm1 #11 [<c0421d38>] __might_sleep+0xbe/0xc5 [<c04770a2>] __munlock_pte_handler+0x3c/0x9e [<c047c11f>] walk_page_range+0x15b/0x1b4 [<c0477048>] __munlock_vma_pages_range+0x4e/0x5b [<c0476f0c>] ? __munlock_pmd_handler+0x0/0x10 [<c0477066>] ? __munlock_pte_handler+0x0/0x9e [<c0477064>] munlock_vma_pages_range+0xf/0x11 [<c0477dcb>] exit_mmap+0x32/0xf2 [<c042ac12>] ? exit_mm+0xc7/0xda [<c042732a>] mmput+0x3a/0x8b [<c042ac20>] exit_mm+0xd5/0xda [<c042bf6a>] do_exit+0x1fb/0x5d5 [<c045c4df>] ? audit_syscall_exit+0x2aa/0x2c5 [<c042c3a3>] do_group_exit+0x5f/0x88 [<c042c3db>] sys_exit_group+0xf/0x11 [<c0403956>] syscall_call+0x7/0xb then, this feature should be disabled on 32BIT until fixed above problem. Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> --- mm/Kconfig | 1 + 1 file changed, 1 insertion(+) Index: b/mm/Kconfig =================================================================== --- a/mm/Kconfig +++ b/mm/Kconfig @@ -216,6 +216,7 @@ config PAGE_WALKER config UNEVICTABLE_LRU bool "Add LRU list to track non-evictable pages" default y + depends on 64BIT select PAGE_WALKER help Keeps unevictable pages off of the active and inactive pageout -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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