[v2,0/2] tty: serial: msm_serial: Fix lockup issues

Message

Leo Yan Nov. 27, 2019, 2:15 p.m. UTC

This patch set is to address two msm serial driver's lockup issues.

The first lockup issue is a well known and common issue which is caused
by recursive locking between normal printing and the kernel debugging
facilities (e.g. sysrq and oops).  Patch 0001 follows up other drivers
general approach to fix this lockup issue.

The second lockup issue is related with msm serial driver's specific
implementation.  Since the serial driver invokes dma related operations
after has acquired spinlock, then the dma functions might allocat dma
descriptors and when the system has very less free memory the kernel
tries to print out warning, this leads to recursive output and causes
deadlock.  Patch 0002 is used to resolve this deadlock issue.

These two patches have been tested on DB410c with backported on 4.14.96,
they also have been verified with mainline kernel for boot testing.

Changes from v1:
* Added 'Fixes' tags for two patches (Jeffrey Hugo).
* Added cover letter for more clear context description (Jeffrey Hugo).


Leo Yan (2):
  tty: serial: msm_serial: Fix lockup for sysrq and oops
  tty: serial: msm_serial: Fix deadlock caused by recursive output

 drivers/tty/serial/msm_serial.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)