scsi: megaraid_sas: Fix concurrent access to ISR between IRQ polling and real interrupt

IRQ polling thread calls ISR after enable_irq() to handle any missed I/O
completion. The atomic flag "in_used" was added to have the synchronization
between the IRQ polling thread and the interrupt context. There is a bug
around it leading to a race condition.

Below is the sequence:

 - IRQ polling thread accesses ISR, fetches the reply descriptor.

 - Real interrupt arrives and pre-empts polling thread (enable_irq() is
   already called).

 - Interrupt context picks the same reply descriptor as fetched by polling
   thread, processes it, and exits.

 - Polling thread resumes and processes the descriptor which is already
   processed by interrupt thread leads to kernel crash.

Setting the "in_used" flag before fetching the reply descriptor ensures
synchronized access to ISR.

Link: https://www.spinics.net/lists/linux-scsi/msg159440.html
Link: https://lore.kernel.org/r/[email protected]
Fixes: 9bedd36e9146 ("scsi: megaraid_sas: Handle missing interrupts while re-enabling IRQs")
Signed-off-by: Sumit Saxena <[email protected]>
Signed-off-by: Martin K. Petersen <[email protected]>

0 files changed, 0 insertions, 0 deletions