Messages in this thread Patch in this message | | | Date | Fri, 23 Apr 2004 04:27:32 +0200 | From | Andrea Arcangeli <> | Subject | Re: Similar behaviour without BUG() message(was: Re: 2.6.5-aa3: kernel BUG at mm/objrmap.c:137!) |
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On Mon, Apr 19, 2004 at 04:32:53PM +0400, Alexander Y. Fomichev wrote: > On Wednesday 14 April 2004 15:47, Andrea Arcangeli wrote: > > ok so there are good chances that 2.6.5-aa5 will fix it, if not then > > please notify me again, thanks. > > I've noticed a behaviour today very similar to mentioned in previous report > (on 14 Apr 2004) except for message from BUG() (kernel 2.6.5-aa5) i.e. > system remained accessible but procps(ps,pkill) appears to be locked and > Sysrq-T is similar to previous one - some of apache2 & all of procps > have been blocked. > > Here is a traces: > > http://sysadminday.org.ru/2.6.5-ps-lockup/sysrq-M > http://sysadminday.org.ru/2.6.5-ps-lockup/full_trace
following your trace I got to some futex issue (likely invoked by NPTL), and following the futex code I noticed a race with threads in expand_stack and likely the futex is effectively calling expand_stack too. Then I found a race in expand_stack with threads.
here the details:
in 2.6-aa expand_stack is moving down vm_start and vm_end with only the read semaphore held. this means this thing can even run in parallel in both cpus, the latter will corrupt vm_pgoff which generate malfunction with anon-vma:
vma->vm_start = address; vma->vm_pgoff -= grow;
this isn't an issue for the file mappings because only anon vmas can be growsdown (the filemappings could never work right in filemap_nopage if expand_stack would mess with pgoff and vm_start without holding the mmap_sem in write mode).
serializing this with anon-vma is easy and scalable with the anon_vma_lock (not an mm-wide lock like the page_table_lock). This will also serialize perfectly with the objrmap. objrmap should be the only thing that cares about vm_pgoff and vm_start being coherent at the same time for anon-mappings in anon-vma, and the anon_vma_lock provides perfect locking for that.
One of the scalability and simplicity locking beauty of anon-vma is the total avoidance of page_table_lock for vma merging and all other vma operations in general, and true usage of page_table_lock only for the pagetables (and future usage of vma->page_table_lock only for pagetables too). I wouldn't really like to giveup on this and to reintroduce the whole mess of page_table_lock in the vma merging and in expand stack that all other implementations like 2.6 mainline and anonmm are suffering from, and I hope my fix will be enough. Could you test if this patch helps?
(there was also an ancient page_table_lock in split_vma, I forgot to delete that previously)
--- 2.6.5-aa3/mm/mmap.c.~1~ 2004-04-14 11:51:33.000000000 +0200 +++ 2.6.5-aa3/mm/mmap.c 2004-04-23 04:04:31.258066752 +0200 @@ -977,6 +977,15 @@ int expand_stack(struct vm_area_struct * return -EFAULT; /* + * We must make sure the anon-vma is allocated + * to make sure the anon-vma locking is not a noop. + */ + if (unlikely(anon_vma_prepare(vma))) + return -ENOMEM; + + anon_vma_lock(vma); + + /* * vma->vm_start/vm_end cannot change under us because the caller * is required to hold the mmap_sem in read mode. We need to get * the spinlock only before relocating the vma range ourself. @@ -986,13 +995,15 @@ int expand_stack(struct vm_area_struct * grow = (address - vma->vm_end) >> PAGE_SHIFT; /* Overcommit.. */ - if (security_vm_enough_memory(grow)) { + if (unlikely(security_vm_enough_memory(grow))) { + anon_vma_unlock(vma); return -ENOMEM; } - if (address - vma->vm_start > current->rlim[RLIMIT_STACK].rlim_cur || - ((vma->vm_mm->total_vm + grow) << PAGE_SHIFT) > - current->rlim[RLIMIT_AS].rlim_cur) { + if (unlikely(address - vma->vm_start > current->rlim[RLIMIT_STACK].rlim_cur || + ((vma->vm_mm->total_vm + grow) << PAGE_SHIFT) > + current->rlim[RLIMIT_AS].rlim_cur)) { + anon_vma_unlock(vma); vm_unacct_memory(grow); return -ENOMEM; } @@ -1000,6 +1011,9 @@ int expand_stack(struct vm_area_struct * vma->vm_mm->total_vm += grow; if (vma->vm_flags & VM_LOCKED) vma->vm_mm->locked_vm += grow; + + anon_vma_unlock(vma); + return 0; } @@ -1028,6 +1042,24 @@ int expand_stack(struct vm_area_struct * unsigned long grow; /* + * We must make sure the anon-vma is allocated + * to make sure the anon-vma locking is not a noop. + */ + if (unlikely(anon_vma_prepare(vma))) + return -ENOMEM; + + /* + * We must serialize against other thread and against + * objrmap while moving the vm_start/vm_pgoff of anon-vmas. + * The total_vm/locked_vm as well needs serialization + * against other threads, the serialization of + * locked_vm/total_vm against syscalls is provided by + * the mmap_sem that we hold in read mode here (all + * syscalls holds it in write mode). + */ + anon_vma_lock(vma); + + /* * vma->vm_start/vm_end cannot change under us because the caller * is required to hold the mmap_sem in read mode. We need to get * the spinlock only before relocating the vma range ourself. @@ -1036,13 +1068,15 @@ int expand_stack(struct vm_area_struct * grow = (vma->vm_start - address) >> PAGE_SHIFT; /* Overcommit.. */ - if (security_vm_enough_memory(grow)) { + if (unlikely(security_vm_enough_memory(grow))) { + anon_vma_unlock(vma); return -ENOMEM; } - if (vma->vm_end - address > current->rlim[RLIMIT_STACK].rlim_cur || - ((vma->vm_mm->total_vm + grow) << PAGE_SHIFT) > - current->rlim[RLIMIT_AS].rlim_cur) { + if (unlikely(vma->vm_end - address > current->rlim[RLIMIT_STACK].rlim_cur || + ((vma->vm_mm->total_vm + grow) << PAGE_SHIFT) > + current->rlim[RLIMIT_AS].rlim_cur)) { + anon_vma_unlock(vma); vm_unacct_memory(grow); return -ENOMEM; } @@ -1051,6 +1085,9 @@ int expand_stack(struct vm_area_struct * vma->vm_mm->total_vm += grow; if (vma->vm_flags & VM_LOCKED) vma->vm_mm->locked_vm += grow; + + anon_vma_unlock(vma); + return 0; } @@ -1289,7 +1326,6 @@ int split_vma(struct mm_struct * mm, str if (mapping) down(&mapping->i_shared_sem); - spin_lock(&mm->page_table_lock); anon_vma_lock(vma); if (new_below) @@ -1301,7 +1337,6 @@ int split_vma(struct mm_struct * mm, str __insert_vm_struct(mm, new); anon_vma_unlock(vma); - spin_unlock(&mm->page_table_lock); if (mapping) up(&mapping->i_shared_sem); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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