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| author |   Peter Zijlstra <a.p.zijlstra@chello.nl> | 2012-06-15 17:43:39 +0200 |
|---|---|---|
| committer |   Ingo Molnar <mingo@kernel.org> | 2012-06-16 09:10:45 +0200 |
| commit | c5784de2b351fe871bb57487878f7fc7ec5b075c (patch) | |
| tree | 4b73571e8fed9af9b6ad6a4cc7f355d0b104a5ea /kernel/events | |
| parent | uprobes: Change build_map_info() to try kmalloc(GFP_NOWAIT) first (diff) | |
| download | linux-dev-c5784de2b351fe871bb57487878f7fc7ec5b075c.tar.xz linux-dev-c5784de2b351fe871bb57487878f7fc7ec5b075c.zip | |
uprobes: Document uprobe_register() vs uprobe_mmap() race
Because the mind is treacherous and makes us forget we need to
write stuff down.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20120615154339.GA9591@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/events')
| -rw-r--r-- | kernel/events/uprobes.c | 31 |
1 files changed, 28 insertions, 3 deletions
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index 897417dbca8e..2671d9ad49be 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -44,6 +44,23 @@ static DEFINE_SPINLOCK(uprobes_treelock); /* serialize rbtree access */ #define UPROBES_HASH_SZ 13 +/* + * We need separate register/unregister and mmap/munmap lock hashes because + * of mmap_sem nesting. + * + * uprobe_register() needs to install probes on (potentially) all processes + * and thus needs to acquire multiple mmap_sems (consequtively, not + * concurrently), whereas uprobe_mmap() is called while holding mmap_sem + * for the particular process doing the mmap. + * + * uprobe_register()->register_for_each_vma() needs to drop/acquire mmap_sem + * because of lock order against i_mmap_mutex. This means there's a hole in + * the register vma iteration where a mmap() can happen. + * + * Thus uprobe_register() can race with uprobe_mmap() and we can try and + * install a probe where one is already installed. + */ + /* serialize (un)register */ static struct mutex uprobes_mutex[UPROBES_HASH_SZ]; @@ -339,7 +356,9 @@ out: int __weak set_swbp(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr) { int result; - + /* + * See the comment near uprobes_hash(). + */ result = is_swbp_at_addr(mm, vaddr); if (result == 1) return -EEXIST; @@ -845,6 +864,10 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register) if (is_register) { err = install_breakpoint(uprobe, mm, vma, info->vaddr); + /* + * We can race against uprobe_mmap(), see the + * comment near uprobe_hash(). + */ if (err == -EEXIST) err = 0; } else { @@ -1054,8 +1077,10 @@ int uprobe_mmap(struct vm_area_struct *vma) } ret = install_breakpoint(uprobe, vma->vm_mm, vma, vaddr); - - /* Ignore double add: */ + /* + * We can race against uprobe_register(), see the + * comment near uprobe_hash(). + */ if (ret == -EEXIST) { ret = 0; |