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Comment about the FILE_IS_RELOCATED flag protection

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Andrea Mazzoleni 2026-05-21 10:28:46 +02:00
parent 65a20f48c6
commit e09e55a01b
1 changed files with 9 additions and 4 deletions
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13
cmdline/scan.c
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@ -308,8 +308,11 @@ static void scan_file_allocate(struct snapraid_scan* scan, struct snapraid_file*
* Delete the specified file from the parity.
*
* Note that the parity remains allocated, but the blocks and the file are marked as DELETED.
* The file is then inserted in the deleted set, and it should not be deallocated,
* as the parity still references it.
*
* The file pointer remain in memory and it's inserted in the deleted set.
*
* It should not be deallocated, as the parity still references it, and other threads
* in the scanning process may reference it when searching for a copy in the "stampset".
*/
static void scan_file_deallocate(struct snapraid_scan* scan, struct snapraid_file* file)
{
@ -1061,8 +1064,9 @@ static void scan_file(struct snapraid_scan* scan, int is_diff, const char* sub,
/*
* Protect the write as multiple threads may write the same FILE_IS_RELOCATED bit.
*
* The bit is always written as 1 and never read, so protection is likely unnecessary
* but still valuable to avoid data race reports from checker tools
* Note that this flag is written in the "shared" portion of the flags,
* intended exactly to avoid data race from multiple threads using
* the stamp_lock() protection.
*/
stamp_lock(other_disk);
file_flag_set(other_file, FILE_IS_RELOCATED);
@ -1737,6 +1741,7 @@ static int state_diffscan(struct snapraid_state* state, int is_diff)
/* remove if not present */
if (!file_flag_has(file, FILE_IS_PRESENT)) {
/* here we are in mono-thread context, no need to use the stamp_lock() to read FILE_IS_RELOCATED */
if (!file_flag_has(file, FILE_IS_RELOCATED)) {
++scan->count_remove;