Reference in a new issue

Blame

Copy permalink

Reference in a new issue

Copy permalink

Vineet Gupta e2e7127ec7 ARC: mm: do_page_fault fixes #1: relinquish mmap_sem if signal arrives while handle_mm_fault ... commit 4d447455e7 upstream. do_page_fault() forgot to relinquish mmap_sem if a signal came while handling handle_mm_fault() - due to say a ctl+c or oom etc. This would later cause a deadlock by acquiring it twice. This came to light when running libc testsuite tst-tls3-malloc test but is likely also the cause for prior seen LTP failures. Using lockdep clearly showed what the issue was. | # while true; do ./tst-tls3-malloc ; done | Didn't expect signal from child: got `Segmentation fault' | ^C | ============================================ | WARNING: possible recursive locking detected | 4.17.0+ #25 Not tainted | -------------------------------------------- | tst-tls3-malloc/510 is trying to acquire lock: | 606c7728 (&mm->mmap_sem){++++}, at: __might_fault+0x28/0x5c | |but task is already holding lock: |606c7728 (&mm->mmap_sem){++++}, at: do_page_fault+0x9c/0x2a0 | | other info that might help us debug this: | Possible unsafe locking scenario: | | CPU0 | ---- | lock(&mm->mmap_sem); | lock(&mm->mmap_sem); | | *** DEADLOCK *** | ------------------------------------------------------------ What the change does is not obvious (note to myself) prior code was | do_page_fault | | down_read() <-- lock taken | handle_mm_fault <-- signal pending as this runs | if fatal_signal_pending | if VM_FAULT_ERROR | up_read | if user_mode | return <-- lock still held, this was the BUG New code | do_page_fault | | down_read() <-- lock taken | handle_mm_fault <-- signal pending as this runs | if fatal_signal_pending | if VM_FAULT_RETRY | return <-- not same case as above, but still OK since | core mm already relinq lock for FAULT_RETRY | ... | | < Now falls through for bug case above > | | up_read() <-- lock relinquished Signed-off-by: Vineet Gupta <vgupta@synopsys.com> [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk>		History 2019-05-02 21:41:24 +01:00
..
cache_arc700.c	ARC: [SMP] Enable icache coherency	2014-06-26 11:59:01 +05:30
dma.c	ARC: I/O and DMA Mappings	2013-02-15 23:15:54 +05:30
extable.c	ARC: Fix coding style issues	2013-04-09 12:21:14 +05:30
fault.c	ARC: mm: do_page_fault fixes #1: relinquish mmap_sem if signal arrives while handle_mm_fault	2019-05-02 21:41:24 +01:00
init.c	ARC: support external initrd	2014-03-26 14:31:27 +05:30
ioremap.c	ARC: Use <linux/*> headers instead of <asm/*>	2013-04-09 12:21:14 +05:30
Makefile	ARC: [mm] Aliasing VIPT dcache support 4/4	2013-05-09 22:00:57 +05:30
mmap.c	mm: larger stack guard gap, between vmas	2017-07-02 17:13:02 +01:00
tlb.c	ARC: Re-enable MMU upon Machine Check exception	2017-11-26 13:50:29 +00:00
tlbex.S	ARC: use ASL assembler mnemonic	2016-11-20 01:17:38 +00:00