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author | Vineet Gupta <vgupta@synopsys.com> | 2018-12-11 01:56:45 +0100 |
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committer | Vineet Gupta <vgupta@synopsys.com> | 2019-01-18 01:24:39 +0100 |
commit | 4d447455e73b47c43dd35fcc38ed823d3182a474 (patch) | |
tree | ed811c74d2bc3ae994e1e4afb460a79c96f5d567 /fs/nfsd/stats.c | |
parent | ARC: show_regs: lockdep: re-enable preemption (diff) | |
download | linux-4d447455e73b47c43dd35fcc38ed823d3182a474.tar.xz linux-4d447455e73b47c43dd35fcc38ed823d3182a474.zip |
ARC: mm: do_page_fault fixes #1: relinquish mmap_sem if signal arrives while handle_mm_fault
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
Cc: stable@vger.kernel.org
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Diffstat (limited to 'fs/nfsd/stats.c')
0 files changed, 0 insertions, 0 deletions