scsi: core: wake eh reliably when using scsi_schedule_eh

Overview

In the Linux kernel, the following vulnerability has been resolved:

scsi: core: wake eh reliably when using scsi_schedule_eh

Drivers which use the scsi_schedule_eh function to run the error handler currently risk the error handler thread never waking once all commands are timed out or inactive. There is no enforced memory order between setting the host into error recovery state and counting busy commands. This can result in a race with scsi_dec_host_busy where neither CPU sees both conditions of all commands inactive and the host error state to request waking the error handler.

To fix this, run the scsi_schedule_eh's scsi_eh_wakeup from a new work item which will use rcu to ensure scsi_schedule_eh's call to scsi_host_busy will occur after the error state is globally visible and will be seen by any current scsi_dec_host_busy callers.

Affected

• Linux >= 6eb045e092efefafc6687409a6fa6d1dabf0fb69 < 4827c824a203eea2c0aa5bfdb13d5c5038cc84da
• Linux >= 6eb045e092efefafc6687409a6fa6d1dabf0fb69 < 866efe8ae8b8b4d095501001b026e1022734be28
• Linux >= 6eb045e092efefafc6687409a6fa6d1dabf0fb69 < c7a15091237205770bd9bd4d14eb1f3029d97a34
• Linux >= 6eb045e092efefafc6687409a6fa6d1dabf0fb69 < 24d7abda6a2a19e113334accc10029f6a4b57257
• Linux >= 6eb045e092efefafc6687409a6fa6d1dabf0fb69 < dccf3b1798b70f94e958b3d00b83010399e6fb05
• Linux 5.5

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.