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FatPkg/EnhancedFatDxe: Ensure traverse of subtasks is delete-safe 

Within function FatQueueTask(), the traverse of FAT subtasks for
executing the disk read/write is not delete-safe.

For the below case:

FatDiskIo(): When non-blocking access, creates subtasks and creates
event (FatOnAccessComplete, NOTIFY level) when subtasks finish.

FatQueueTask(): Traverses the subtasks and submits them one by one at
Tpl lower than NOTIFY.

Disk R/W completes really quick.

FatOnAccessComplete(): Removes the finished subtask, causing the
traverse in FatQueueTask() broken.

This commits will refine the subtask traverse in FatQueueTask() to be
delete-safe.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
This commit is contained in:
Hao Wu 2018-04-14 11:06:13 +08:00
parent 104bbee55e
commit 2551014719
1 changed files with 12 additions and 3 deletions
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15
FatPkg/EnhancedFatDxe/Misc.c
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@ -132,6 +132,7 @@ FatQueueTask (
{ {
EFI_STATUS Status; EFI_STATUS Status;
LIST_ENTRY *Link; LIST_ENTRY *Link;
LIST_ENTRY *NextLink;
FAT_SUBTASK *Subtask; FAT_SUBTASK *Subtask;
// //
@ -149,9 +150,17 @@ FatQueueTask (
EfiReleaseLock (&FatTaskLock); EfiReleaseLock (&FatTaskLock);
Status = EFI_SUCCESS; Status = EFI_SUCCESS;
for ( Link = GetFirstNode (&Task->Subtasks) //
; !IsNull (&Task->Subtasks, Link) // Use NextLink to store the next link of the list, because Link might be remove from the
; Link = GetNextNode (&Task->Subtasks, Link) // doubly-linked list and get freed in the end of current loop.
//
// Also, list operation APIs like IsNull() and GetNextNode() are avoided during the loop, since
// they may check the validity of doubly-linked lists by traversing them. These APIs cannot
// handle list elements being removed during the traverse.
//
for ( Link = GetFirstNode (&Task->Subtasks), NextLink = GetNextNode (&Task->Subtasks, Link)
; Link != &Task->Subtasks
; Link = NextLink, NextLink = Link->ForwardLink
) { ) {
Subtask = CR (Link, FAT_SUBTASK, Link, FAT_SUBTASK_SIGNATURE); Subtask = CR (Link, FAT_SUBTASK, Link, FAT_SUBTASK_SIGNATURE);
if (Subtask->Write) { if (Subtask->Write) {