Commit b5066102 authored by Andi Kleen's avatar Andi Kleen Committed by Linus Torvalds

[PATCH] x86-64: avoid deadlock in page fault handler

Avoid deadlock when kernel fault happens inside mmap sem.
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 668174af
......@@ -315,7 +315,27 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long error_code)
goto bad_area_nosemaphore;
again:
down_read(&mm->mmap_sem);
/* When running in the kernel we expect faults to occur only to
* addresses in user space. All other faults represent errors in the
* kernel and should generate an OOPS. Unfortunatly, in the case of an
* erroneous fault occuring in a code path which already holds mmap_sem
* we will deadlock attempting to validate the fault against the
* address space. Luckily the kernel only validly references user
* space from well defined areas of code, which are listed in the
* exceptions table.
*
* As the vast majority of faults will be valid we will only perform
* the source reference check when there is a possibilty of a deadlock.
* Attempt to lock the address space, if we cannot we then validate the
* source. If this is invalid we can skip the address space check,
* thus avoiding the deadlock.
*/
if (!down_read_trylock(&mm->mmap_sem)) {
if ((error_code & 4) == 0 &&
!search_exception_tables(regs->rip))
goto bad_area_nosemaphore;
down_read(&mm->mmap_sem);
}
vma = find_vma(mm, address);
if (!vma)
......
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