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mm: remove the now-unnecessary mmget_still_valid() hack

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The preceding patches have ensured that core dumping properly takes the
mmap_lock.  Thanks to that, we can now remove mmget_still_valid() and all
its users.

Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: "Eric W . Biederman" <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Link: http://lkml.kernel.org/r/20200827114932.3572699-8-jannh@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jann Horn
2020-10-15 20:13:00 -07:00
committed by Linus Torvalds
parent 7f3bfab52c
commit 4d45e75a99
8 changed files with 32 additions and 110 deletions
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25
include/linux/sched/mm.h
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@@ -49,31 +49,6 @@ static inline void mmdrop(struct mm_struct *mm)
__mmdrop(mm);
}
/*
* This has to be called after a get_task_mm()/mmget_not_zero()
* followed by taking the mmap_lock for writing before modifying the
* vmas or anything the coredump pretends not to change from under it.
*
* It also has to be called when mmgrab() is used in the context of
* the process, but then the mm_count refcount is transferred outside
* the context of the process to run down_write() on that pinned mm.
*
* NOTE: find_extend_vma() called from GUP context is the only place
* that can modify the "mm" (notably the vm_start/end) under mmap_lock
* for reading and outside the context of the process, so it is also
* the only case that holds the mmap_lock for reading that must call
* this function. Generally if the mmap_lock is hold for reading
* there's no need of this check after get_task_mm()/mmget_not_zero().
*
* This function can be obsoleted and the check can be removed, after
* the coredump code will hold the mmap_lock for writing before
* invoking the ->core_dump methods.
*/
static inline bool mmget_still_valid(struct mm_struct *mm)
{
return likely(!mm->core_state);
}
/**
* mmget() - Pin the address space associated with a &struct mm_struct.
* @mm: The address space to pin.